Measuring for curtains is easier when you separate the job into three decisions: where the hardware will sit, how much fabric the window needs, and how the finished curtain should fall. This room-by-room guide explains how to measure inside- and outside-mount windows, calculate panel width and fullness, allow for stack-back space, and avoid common sizing mistakes. Save the worksheet at the end so you can reuse it for future window treatments.
Overview
Before measuring, decide whether the curtain will hang from a pole or track and whether the hardware will be mounted inside the window recess or outside it. Measure every window individually, even when several windows appear identical. Small differences in frame width, sill depth, or ceiling height can affect the final fit.
You will need a steel tape measure, a pencil, paper, and a step ladder if the hardware will be mounted high. Record measurements in the same unit throughout the project. For made-to-measure curtains, follow the supplier's measuring instructions before ordering, because some manufacturers request finished curtain dimensions while others request pole or track dimensions.
Inside mount or outside mount?
An inside mount places the pole or track within the window recess. It can suit deep, square recesses and gives a neat, built-in appearance, but it may allow more light around the edges and leaves less room for lining, brackets, or bulky curtain headings. Check that the recess is deep enough for the chosen hardware and fabric.
An outside mount places the hardware on the wall above and beyond the window frame. This approach is usually more forgiving, can make a window appear taller and wider, and is useful when the recess is shallow or uneven. It also creates more space for blackout or thermal curtains to overlap the window.
The core formulas
For the finished curtain width, use:
Required fabric width = curtain pole or track width × fullness factor
As a practical starting point, use a fullness factor of about 1.5 to 2 for many ready-made or gathered curtains. Sheer curtains and lightweight fabrics often look better with more fullness, while heavy fabrics may require less. The heading style and the manufacturer's instructions can change the calculation.
To estimate the number of panels:
Number of panels = required fabric width ÷ width of one panel
Round up to a whole panel. If the result is close to the next whole number, choosing the additional panel generally provides a fuller appearance than trying to stretch too little fabric across the window.
Template structure
1. Measure the pole or track width
For an existing pole or track, measure from one end to the other, excluding decorative finials unless the curtains must cover them. For a new outside mount, measure the window or door opening, then add the space needed for the curtain to clear each side. The exact allowance depends on wall space, furniture, radiators, handles, and the curtain's stack-back.
Stack-back is the amount of curtain that gathers to the side when open. A wide window may need substantial side space, particularly with lined, blackout, velvet, or other dense fabrics. If the panels would cover too much glass when open, consider a wider pole, a split track, or a different opening arrangement.
2. Measure the drop
Measure from the point where the curtain will hang to the intended bottom position. Take at least three vertical measurements—left, centre, and right—because floors, ceilings, and recesses are not always level. Use the shortest measurement for a floor-skimming finish when the floor varies noticeably.
For a pole, measure from the underside of the rings or from the top of the curtain heading, depending on how the curtain attaches. For a track, measure from the top of the track or the glider position according to the heading design. Do not automatically measure from the ceiling unless the hardware will actually be installed there.
3. Choose the bottom finish
- Sill length: Finish slightly above the sill so the fabric does not rest on it.
- Below-sill length: Extend beyond the sill for a more generous look, while keeping the fabric clear of nearby furniture or heaters.
- Floor length: Finish just above the floor, or close to it, for a clean everyday drop.
- Puddle or break: Allow extra length only when the decorative finish is intentional and the fabric can be maintained safely.
A curtain length guide is useful, but the room should decide the final measurement. In bedrooms, living rooms, and dining rooms, floor-length curtains often create continuity. In kitchens, bathrooms, or rooms with obstructions, a shorter washable curtain may be more practical.
4. Allow for headings and hems
Ready-made curtain labels may state the total panel size, while custom curtain forms may ask for the finished drop. Confirm whether the stated measurement includes the heading, eyelets, tabs, or hem. Pinch pleat curtains, grommet curtains, and curtains with hidden tabs can each hang at a different height from the same pole.
Printable measuring worksheet
Copy this record for each window:
- Room and window name:
- Mount: inside recess or outside mount:
- Hardware: pole or track:
- Window or door opening width:
- Chosen pole or track width:
- Left, centre, and right drop:
- Finished drop required:
- Panel width:
- Fullness factor:
- Number of panels:
- Heading style:
- Obstructions: handles, radiators, furniture, shutters, or skirting:
- Fabric care or shrinkage notes:
How to customize
Room-by-room adjustments
For living room curtains, prioritize the relationship between the window, furniture, and walking route. Check that panels do not block doors, conceal radiators, or catch on shelving. Large windows may need a wider track, centre opening, or multiple panels to distribute weight evenly.
For bedroom curtains, measure for the light control you actually need. Blackout or thermal curtains generally benefit from an outside mount with overlap beyond the frame, although no curtain arrangement eliminates every possible light gap. If layering sheer curtains with a heavier curtain, measure the front and rear tracks separately and check that the brackets provide enough clearance.
For nursery curtains, record the position of cots, changing furniture, and accessible cords before choosing the hardware. Look for a secure installation plan and follow the product's safety instructions. A washable curtain can be useful where regular cleaning is expected; see the nursery curtain guide for related considerations.
For patio door curtains, measure the full opening and confirm which door swings or slides. Leave clearance for handles and allow the curtain to stack away from the active door panel. A split draw arrangement can keep the opening usable, while a single panel may work better where wall space is limited. French doors require similar attention to handle clearance and mounting depth; review these French door mounting solutions before ordering.
Bay windows and unusual shapes
Do not treat a bay window as one straight opening unless the hardware is designed for that configuration. Measure each bay section, note the angle between sections, and check where brackets can be fixed. Flexible tracks, separate poles, or made-to-measure systems may be appropriate depending on the shape and desired opening. For angled or unusually shallow bays, a professional measurement service can reduce the risk of ordering incompatible hardware.
Account for fabric behavior
Fabric type affects both appearance and usable space. Linen curtains may soften or relax over time; velvet curtains are dense and can need more room at the sides; sheer curtains often need additional fullness to avoid looking sparse. If a fabric can shrink, check its care instructions and ask whether it has been prewashed. Sustainable curtains and natural-fibre textiles should be measured with the same care as any other fabric, but their care and dimensional stability may differ by product.
Examples
Example 1: outside-mounted living room curtains
Suppose the chosen pole measures 240 cm and you want a fullness factor of 1.8. The required fabric width is 240 × 1.8, or 432 cm. If each ready-made panel is 135 cm wide, divide 432 by 135 to get 3.2 panels. Round up to four panels, usually arranged as two pairs, to achieve the planned fullness and a balanced centre opening.
Example 2: a small bedroom window
A shallow recess may suit an outside-mounted track. Measure beyond both sides of the frame only as far as wall space allows, then confirm that the opened curtain will not cover a bedside table or obstruct a wardrobe. Choose a floor drop only if the fabric will remain clear of the furniture and floor-level vents. Otherwise, a sill or below-sill finish may be easier to live with.
Example 3: a patio door
Measure the track width across the usable wall area, not just the glass. Mark the active door swing or slide, handle projection, and the side where the curtain will stack. Calculate width using the track measurement and selected fullness, then confirm that the finished panels can move fully clear of the opening.
For a second calculation, use the site's curtain measurement calculator and length guide. If you are comparing panel quantities or heading styles, the curtain fullness guide provides a useful companion reference.
When to update
Revisit your measurements whenever the underlying conditions change: after replacing a window, adding insulation, changing a radiator, moving furniture, installing shutters, or switching from a pole to a track. Recheck the measurements before every new order rather than relying on an old worksheet.
Before installation, compare the product's stated dimensions with your notes, inspect the heading and hardware, and confirm the fixing points. Measure once more after the pole or track is securely installed if the final drop depends on its exact position. Mark the intended bracket locations, use fixings suited to the wall, and avoid drilling into hidden services.
For future projects, keep the worksheet, a photo of the window, and the product instructions together. This simple record makes it easier to replace panels, add a second layer, or compare custom curtains with ready-made curtains without starting from zero.
Final checklist: measure each window separately; decide inside or outside mount; record three drop measurements; calculate width from the pole or track; allow for fullness and stack-back; check handles, radiators, furniture, and doors; confirm how the product defines its dimensions; and review the result before ordering.
