How to Measure Curtains Correctly for Your Windows

Measuring curtains correctly involves more than running a tape measure across the window frame. The final fit depends on where the curtain track or rod will sit, how far the curtains need to extend beyond the window, the chosen heading style, the finished curtain drop and the amount of space required when the curtains are open. Getting these details right is the difference between a polished window treatment and one that looks flat, too short or poorly fitted.

To measure curtains correctly, first decide where the track or rod will be installed. Measure the proposed installation width, including space on each side for the curtains to stack, and then measure the finished drop from the track or rod to the desired endpoint. Record every measurement in millimetres and check the width and drop more than once before ordering.

This guide explains the process step by step, including how to measure sheers, blackout curtains, layered window treatments and curtains for sliding doors.

What You Need Before Measuring Your Windows

You do not need specialist equipment for a straightforward window, but the right tools make errors less likely.

Prepare:

• A steel measuring tape
• A pencil and measurement sheet
• A stable step ladder
• A spirit level
• A laser measure for tall or wide windows
• A mobile phone for reference photos
• Another person for large doors or wall-to-wall installations

Use millimetres for every measurement. Millimetres provide better accuracy and reduce confusion when your measurements are given to a curtain manufacturer or installer.

Label each room and window clearly. If you are measuring an entire house, descriptions such as “Window 1” quickly become confusing. Use labels such as “main bedroom window beside wardrobe” or “living room sliding door”.

Builders, contractors and small-business owners measuring several openings should photograph each window with the measurement sheet visible in the frame. This makes it easier to match the dimensions with the correct opening later.

Can I use my phone to measure a window?

Some smartphones support augmented-reality measuring apps that can estimate window dimensions. However, accuracy varies and these apps are not reliable enough for ordering custom curtains. Phone measurements work well as a rough reference or for confirming you are in the right ballpark, but a steel tape measure remains the only tool accurate enough for millimetre-precise curtain measurements. Even a few millimetres of error across a wide window can affect how the curtains hang and close.

Decide How the Curtains Will Be Mounted

Before measuring the curtains, decide where the hardware will sit. The position of the track or rod determines both the finished width and curtain drop.

Common installation options include:

• Ceiling-mounted curtain tracks
• Wall-mounted tracks above the window
• Decorative curtain rods
• Wall-to-wall tracks
• Floor-to-ceiling curtains
• Tracks fitted inside a pelmet or ceiling recess

A ceiling-mounted track can make the room feel taller and create a cleaner finish. A wall-mounted rod may suit a traditional interior or an existing window arrangement. Neither option is automatically better; the right choice depends on the room, ceiling structure, furniture placement and curtain style.

When comparing curtain tracks and poles, think about more than appearance. Tracks and rods can require different curtain drop measurements, heading styles and mounting clearances.

If no hardware has been installed, do not measure only the window and order the curtains immediately. First decide:

• How high the track will sit
• How far it will extend beyond the frame
• Whether the curtains will open from the centre or one side
• Whether a second track is needed for sheers or blockout curtains
• Whether there is enough wall or ceiling support for the hardware

Understand the Four Width Measurements People Commonly Confuse

One of the most common curtain-measuring mistakes is treating every width measurement as the same number. The curtain heading style you choose also affects how wide the fabric needs to be, so it is worth understanding these four dimensions before taking any measurements.

1. Glass width

This is the visible glass area. It is rarely the final curtain measurement because curtains normally need to cover the frame and extend beyond it.

2. Window-frame width

This is the measurement from the outside edge of one side of the frame to the other. It is a useful reference, but it may still be narrower than the planned curtain track.

3. Track or rod width

This is the usable width across which the curtains will move. It normally extends beyond the window frame to provide better coverage and stack-back space.

4. Finished curtain or fabric width

This is not necessarily the same as the track width. The curtain maker calculates the fabric required according to the track size, heading style, fullness and fabric type.

For example, imagine a window frame that is 1,800 mm wide. The planned track may be 2,200 mm wide so the open curtains can sit partly against the wall rather than covering the glass. The total fabric used may be considerably wider again because it needs to form pleats or waves depending on the curtain heading selected.

When ordering custom curtains, it is generally safer to provide the confirmed track or installation width and allow the curtain specialist to calculate the fabric requirement.

How to Measure Curtain Width Correctly

Start by deciding whether you are measuring existing hardware or planning a new installation.

Measuring an existing curtain track

Measure the usable track from one end to the other. Do not include decorative covers or parts of the track that the curtain carriers cannot reach.

Check whether the track is straight and level. An older track may have shifted slightly, especially across a wide sliding door.

Also record the opening direction:

• Centre opening
• Stack to the left
• Stack to the right

This affects how the curtains are manufactured and where the fabric sits when open.

Measuring an existing curtain rod

Measure the usable rod width between the decorative finials. The finials are the ornamental ends of the rod and are not normally part of the curtain’s travelling area.

Check how the curtains will attach. Eyelet curtains, curtain rings and pleated curtains can each have a different starting point for the finished drop.

Measuring when no track or rod is installed

Measure the window-frame width first. Then check how much clear wall space is available on both sides.

The track should usually extend beyond the frame so the curtains provide proper coverage when closed and do not cover too much glass when open. The exact extension depends on:

• Curtain fabric thickness
• Curtain heading style
• Window width
• Available wall space
• Whether the curtains are single or layered
• Whether they open from the centre or one side

Do not assume the same extension will suit every window. A lightweight sheer curtain requires different stack space from a heavy lined curtain.

How to Measure Curtain Drop Correctly

The curtain drop is the vertical measurement from the chosen starting point to the desired finished length.

The starting point depends on the hardware and curtain style. It might be:

• From the underside of a ceiling track
• From the top or bottom of a track
• From the bottom of a curtain ring
• From the top of a curtain rod
• From a specific hook position

Confirm which starting point your curtain supplier requires before submitting the measurement.

Measure the drop in at least three places:

1. Left side
2. Centre
3. Right side

Floors and ceilings are not always perfectly level. A difference of only several millimetres can become noticeable when a curtain runs across an entire wall.

Do not automatically average the three measurements. Record each number and let the curtain manufacturer or installer determine the most suitable finished drop.

Quick conversion: A 183 cm curtain drop equals 72 inches (6 feet), which is a common ready-made standard size. Custom-made curtains allow you to specify the exact drop in millimetres rather than working around standard sizing, which is particularly useful when floors or ceilings are not perfectly level.

Choosing the finished curtain length

Curtains can finish in several ways.

Above the windowsill: Practical for small windows, kitchens or areas where furniture sits below the window.

Below the windowsill: Provides more coverage but still keeps the curtain clear of the floor.

Floor clearance: The curtain finishes slightly above the floor, making it easier to open, close and clean around.

Floor-kiss finish: The fabric finishes very close to the floor for a tailored appearance.

Small fabric break: The curtain touches the floor with a slight fold.

Pooling: Extra fabric rests deliberately on the floor for a softer, more luxurious look.

Are curtains better too long or too short?

Curtains that are slightly too long are generally more forgiving than curtains that are too short. A small floor break or gentle pool is easy to manage and often reads as intentional, while a curtain that sits noticeably above the floor tends to look like a measuring error. For a tailored result, aim for a floor-kiss finish or a slight clearance rather than ordering conservatively short.

A floor-kiss finish suits a formal living room, but a small clearance is more practical in a busy household with pets, children or a robotic vacuum. For offices, shops and commercial spaces, a slight floor clearance is generally easier to maintain.

How Much Wider Should Curtains Be Than the Window?

Curtains are usually wider than the window opening because they need fabric fullness and enough coverage around the frame.

Fullness refers to the extra fabric that creates the curtain’s folds, pleats or waves. Without sufficient fullness, the curtains can look flat and stretched when closed.

However, there is no single multiplier that suits every curtain. The required amount depends on:

• Curtain heading style
• Fabric weight
• Fabric transparency
• Track system
• Finished appearance
• Manufacturer specifications

Sheers often use generous fullness to create soft, continuous folds. A fixed pinch-pleat curtain is manufactured differently from a pencil-pleat curtain that is gathered after installation. S-fold curtains depend on the spacing of the carriers in the track.

Avoid multiplying the window width yourself unless the supplier specifically asks for fabric width. For custom curtains, provide the finished track width and curtain heading style so the manufacturer can make the correct calculation.

Allow Enough Space for Curtain Stack-Back

Stack-back is the amount of space occupied by the curtains when they are fully open.

It matters because a curtain track that finishes at the edge of the window may leave the open fabric covering a large section of the glass.

Before deciding the track width, ask:

When the curtains are open, should they cover part of the glass or sit mostly against the wall?

To answer that question, measure the clear wall space beside the window.

Look for anything that could restrict the stack, including:

• Light switches
• Power points
• Artwork
• Built-in shelves
• Wardrobes
• Air-conditioning units
• Doors opening towards the curtain
• Furniture placed beside the window

A centre-opening curtain divides the stack between both sides. A one-way curtain places all the fabric on one side and therefore needs more space in that location.

For example, a sliding door used mainly from the right may work better with the curtain stacking to the left. This keeps the main access point clear and reduces the chance of people handling the fabric every time they walk through the door.

How to Measure Different Curtain Styles

Different curtain headings require different information.

Curtain style	Main measurements	Additional considerations
S-fold or wave-fold	Finished track width and drop	Carrier spacing, track type and stack-back
Pencil pleat	Track or rod width and drop	Gathering allowance
Pinch pleat	Finished coverage width and drop	Fixed pleats and opening direction
Eyelet curtain	Rod width and finished drop	Rod diameter, eyelet position and finials
Sheer curtain	Track width, drop and stack area	Transparency, fullness and layering
Blackout curtain	Coverage width, drop and side gaps	Light entering around the curtain edges

The main lesson is simple: measure the installation, not the amount of fabric. The curtain maker should calculate pleats, waves and fullness according to the selected curtain heading.

You can explore different custom curtain options before confirming the measurements, as the chosen curtain style may change the hardware and space requirements.

How to Measure for Sheer Curtains

Sheer curtains are often installed from ceiling to floor and may run across an entire wall rather than covering only the window. As a complete window treatment they work best when planned as a full system rather than an afterthought.

Start by measuring the proposed full track width. Then measure the drop from the track position to the finished point at the left, centre and right.

Also decide:

• Will the sheers open from the centre or one side?
• Will they cover one window or the entire wall?
• Will a blockout curtain or blind sit behind them?
• Is there enough room for the fabric to stack?
• Are there door handles or window winders behind the fabric?

Homeowners comparing sheer curtains should confirm whether the quoted dimensions refer to the window, track, finished curtain or total fabric width. These figures are not interchangeable.

For a soft, full-height finish, browse custom sheer curtains before deciding the track position and opening style.

Example: wall-to-wall living-room sheers

Imagine a living room with a 2,100 mm window centred on a 3,600 mm wall. Measuring only the window would produce a very different result from installing a wall-to-wall ceiling track.

A wall-to-wall sheer creates a broader, more balanced window treatment, but the measurements must account for the full wall width, skirting boards, nearby furniture and the fabric stack at each end.

How to Measure for Blackout Curtains

Blackout curtains need careful coverage around the opening. Even a well-made blackout fabric cannot reduce light effectively if there are large gaps above, below or beside the curtain.

When measuring, check:

• How far the track extends beyond the window frame
• Whether light can enter above the track
• Whether the fabric will clear the floor
• Whether the curtain needs to overlap a deep windowsill
• Whether handles or winders project from the window
• Whether a pelmet is being considered
• Whether sheers will sit on a second track

When measuring for blackout curtains, consider the entire opening rather than just the glass. Extending the curtain past the frame reduces side light, while a ceiling-mounted track or pelmet helps manage light entering above. No curtain should be described as creating complete darkness unless the entire window treatment system has been designed to control light gaps.

For a layered option, review sheers with blockout linings.

How to Measure Layered Sheer and Blackout Curtains

Layered curtains usually require two tracks. One layer provides daytime softness and privacy, while the second provides stronger privacy and light control at night. Together they form a complete window treatment that needs to be measured as a single system.

Measure each layer as part of that complete system.

Check:

• Total track width
• Curtain drop for the sheer layer
• Curtain drop for the blockout layer
• Distance between the two tracks
• Total projection from the wall
• Clearance from handles and window frames
• Stack-back space for both layers
• Recess or pelmet dimensions
• Opening direction for each curtain

The two drops may not be identical. The curtain heading, hook position and track arrangement can change where each fabric starts.

A double-track system also projects farther into the room. This matters when curtains sit near a deep windowsill, door handle or built-in cabinet.

For rooms where a blind will provide the blockout layer, blockout roller blinds with sheer curtains can offer an alternative to two fabric curtain layers.

Should You Measure Curtains and Roller Blinds Differently?

Yes. Curtains are usually measured according to the track or rod position, while roller blinds are measured according to whether they sit inside or outside the window recess.

An inside-mounted roller blind needs accurate recess measurements at several points because walls and frames may not be perfectly square. An outside-mounted blind needs additional coverage beyond the opening.

When planning a combined window treatment for example, a roller blind sitting behind a sheer curtain check that:

• The blind mechanism fits within or above the recess
• The curtain clears the blind and its brackets
• Both products can operate independently
• The curtain track projects far enough from the wall

Explore custom roller blinds when comparing layered window-treatment options.

How to Measure Curtains for Sliding and Bi-Fold Doors

Sliding and bi-fold doors need more planning than a standard window because the curtains must not interfere with everyday access.

Measure the complete door opening, not just one panel.

Then identify:

• The panel used most often
• The direction in which the door opens
• The location of the handle
• The best curtain opening direction
• The available stack space
• The floor level across the opening
• The curtain’s clearance from the door track

Example: a 2,400 mm sliding door

Consider a 2,400 mm sliding door with 650 mm of clear wall space on the left and 450 mm on the right. The household normally enters through the right-hand side.

A centre-opening curtain would place fabric near the main access point. A one-way curtain stacking to the left may be more practical because it keeps the frequently used side clear.

If both sheers and blockout curtains are planned, the measurement must also allow for a double track, separate stack-back requirements and the projection of the door handle.

For very wide doors, a motorised curtain system may make daily operation easier.

How to Measure Bay Windows, Corner Windows and Compact Spaces

Bay windows and corner windows should not be treated as one flat opening.

Measure each section separately and record:

• The width of every window section
• Internal and external angles
• The available fixing surface
• The location of track joins
• The curtain drop at several points
• The direction in which the curtains will move
• The available stack space

A track may need to be bent or joined to follow the shape. Small inaccuracies in the angles can affect how smoothly the curtain travels around the corner.

Compact rooms and tiny homes require similar care. A poorly planned stack can cover a large portion of a small window or interfere with storage, seating and doors.

For example, in a tiny home with a window beside a built-in dining seat, a full curtain stack may not fit on both sides. A one-way opening, roller blind or shorter curtain could be more practical.

Check for Obstacles Before Finalising the Measurements

Stand back and inspect the entire area around the window.

Check for:

• Window and door handles
• Skirting boards
• Deep windowsills
• Air conditioners
• Heating vents
• Power points
• Light switches
• Furniture
• Cabinets
• Cornices
• Bulkheads
• Existing blinds or shutters
• Security sensors
• Uneven ceilings or floors

Do not simply note that an obstacle exists. Measure how far it projects from the wall.

A window handle that projects 70 mm may require the curtain track to sit farther into the room. A skirting board can also affect a wall-to-wall window treatment if the fabric is expected to hang very close to the wall.

Common Curtain-Measuring Mistakes to Avoid

The most frequent errors are usually simple ones:

• Measuring only the visible glass
• Confusing frame width with track width
• Measuring before choosing the hardware
• Recording some measurements in centimetres and others in millimetres
• Measuring the curtain drop in only one place
• Forgetting stack-back
• Ignoring handles and skirting boards
• Adding a generic fullness multiplier
• Failing to choose the opening direction
• Assuming matching windows have identical dimensions
• Ordering before checking whether the ceiling or wall is level
• Forgetting planned flooring changes
• Providing fabric width when the supplier requires track width

Measure every opening individually, even when two windows appear to be the same size.

Worked Example: Measuring a Sliding Door for Sheers and Blackout Curtains

This worked example shows how to measure curtains correctly for a sliding door with two layers.

Consider a living room with the following layout:

• Sliding-door opening: 2,400 mm
• Ceiling height: 2,700 mm
• Clear wall space on the left: 650 mm
• Clear wall space on the right: 450 mm
• Main access point: right side
• Curtain treatment: sheer and blockout layers
• Proposed hardware: double ceiling track

The first decision is the opening direction. Because the household regularly uses the right side of the door, a one-way curtain stacking to the left may provide better access than a centre-opening curtain.

Next, the proposed track width must account for the door opening and available stack space. The installer also needs to check whether the 650 mm section on the left contains switches, artwork or furniture.

The curtain drop should be measured at the left, centre and right from the proposed ceiling-track position. The door-handle projection should also be recorded to ensure the rear curtain layer does not catch.

The sheer and blackout curtains may need separate finished drops because they sit on different tracks with different heading positions.

This example shows why a 2,400 mm door opening does not automatically mean ordering 2,400 mm-wide curtains. The final specification depends on the track, heading, stack, hardware and opening direction.

Curtain Measurement Checklist

Use this checklist every time you measure curtains for a new window or door. Recording the curtain drop in three places left, centre and right is especially important, as floors and ceilings are rarely perfectly level.

Measurement detail	Record here
Room name
Window or door type
Window-frame width
Proposed track width
Wall space on the left
Wall space on the right
Curtain drop on the left
Curtain drop in the centre
Curtain drop on the right
Track or rod type
Curtain heading style
Centre or one-way opening
Sheer, blackout or layered curtains
Existing blinds or shutters
Largest wall projection
Photos taken	Yes / No

For double-track or layered window treatment installations, record a separate set of drop measurements for each layer and note the distance between the two tracks.

Not sure your measurements are right before ordering? Book a free measure and quote a specialist will confirm your track width, curtain drop and stack-back on-site before manufacturing begins.

When Should You Book a Professional Curtain Measure?

DIY measuring can work well for a straightforward window with existing hardware. Professional measuring is usually worthwhile when the project involves:

• Ceiling-to-floor curtains
• Uneven floors or ceilings
• Very wide or tall openings
• Double tracks
• Bay or corner windows
• Sliding or bi-fold doors
• Motorised curtains
• Recessed tracks or pelmets
• Several rooms in a new build
• A commercial or office fit-out

A professional measure can confirm the mounting surface, track width, finished curtain drop, stack-back, opening direction and clearances before the curtains are manufactured.

Get the Measurements Confirmed Before Ordering

Measuring curtains correctly means accounting for the complete window treatment not only the size of the window. Track position, finished curtain drop, curtain heading, stack-back, floor level and surrounding obstacles all influence the final result.

For custom advice, book a free measure and quote with Curtains Direct and have your window openings, hardware requirements and curtain style assessed before manufacturing begins.