Key takeaways
- Map a projecting sill, hardware position and curtain folds in a side view before deciding whether your curtain can hang freely.
What's inside
To measure curtains around a projecting window sill, record two things separately: the vertical drop and the horizontal space occupied by the fabric. A curtain can have the right length yet catch on the sill because its folds sit too close to the wall. Draw a side view before deciding that a longer curtain or a deeper bracket will solve the problem.
The aim is a useful measurement brief for your existing hardware or installer. This is not a bracket installation guide, a load calculation or permission to cover a heater. Where heat, ventilation or an opening window is involved, the relevant equipment and window requirements take priority.
Establish a wall reference
Start with the wall surface above and beside the window as your reference plane. Sketch the sill sticking out from it. Measure the furthest projection, including trim that extends beyond the main sill, and label that number. Check both ends and the middle rather than assuming the projection is identical everywhere.
Next record the handle, any protruding latch and the path of the opening sash. A sill may be the most obvious obstruction without being the largest one. Keep fixed projections and moving parts in separate notes. Do not measure a window only in its closed position if you expect to open it while the curtains remain in place.
Locate the fabric, not just the bracket end
Identify the actual point from which your chosen heading hangs. A bracket’s advertised projection is not necessarily the distance to the nearest fold of cloth. Pole centres, rings, hooks and heading shape all affect where the fabric sits relative to the wall.
John Lewis’s curtain measuring guide recommends fitting the track or pole before taking final curtain measurements. It also distinguishes the measuring reference for pencil pleats from that for eyelets. Its eyelet guidance specifies a bracket projection of at least 10 cm for the folds to move freely; that is its heading guidance, not a guarantee that 10 cm clears your particular sill.
For existing curtains, observe the closest fold to the wall while the curtain is closed, partly drawn and gathered at the side. For a new system, obtain the supplier’s heading and hardware drawing or arrange a sample. A string hanging from a pole can show a straight reference line, but it cannot reproduce the depth of a gathered fabric fold.
Fill in a side-view worksheet
| Feature | Measurement or observation | What it controls |
|---|---|---|
| Sill front | Furthest distance from wall | Fixed obstruction below the fabric |
| Handle or latch | Closed and operating positions | Local snag or opening conflict |
| Hanging reference | Track, ring eye or other specified point | Start of the finished drop |
| Nearest fabric fold | Observed or confirmed distance from wall | Whether cloth reaches the sill |
| Chosen finish | Above sill, below sill or floor | Required vertical length |
Add a small sketch beside the worksheet and mark which measurements are confirmed and which are still estimates. Keep the units consistent. Record the equipment model when a track, bracket or heading specification is used, so an installer can tell exactly which arrangement you have evaluated.
Choose the finish only after checking the path
An above-sill curtain stops before reaching the obstruction. A below-sill or floor-length curtain needs a clear route past it. These are different geometric solutions, not interchangeable lengths of the same drawing. Compare them against the window’s use and the appearance you want.
Do not pull cloth tightly around the sill to make a measurement work. That changes the shape and may prevent easy movement. If the planned curtain cannot pass freely, discuss a compatible hardware arrangement, a different heading or an alternative finish with the supplier. Extending a bracket also changes the installation’s demands, so do not assume an unapproved extension is acceptable.
A worked example with a projecting sill
Imagine a sill projecting 8 cm from the wall. The proposed hardware puts the hanging reference 12 cm from that wall. At first glance there appears to be 4 cm available. However, a supplier’s sample shows the nearest part of the chosen fold sitting 5 cm behind that reference, at 7 cm from the wall.
In this illustrative geometry, 7 cm is closer to the wall than the sill front at 8 cm, so the fabric path overlaps the sill. The 4 cm subtraction alone gave the wrong impression because it ignored the fold. These invented dimensions demonstrate the check; they are not recommended clearances or a specification for any product.
Confirm the complete moving arrangement
Before ordering, check the curtain at its full proposed width and heading, including the gathered stack at each end. Confirm that it can be drawn without snagging the handle or dragging across the sill. Check access for normal window operation and cleaning, while keeping any required ventilation clear.
Then take the final drop from the heading reference specified by the supplier to the chosen finish. Save the side-view sketch with the order. If the hardware changes later, recheck both the horizontal fabric path and the drop; the previous curtain length alone does not confirm that the new arrangement fits.
