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How to Measure Your Windows for Curtains (DIY Guide)
Measure your windows like a pro: where to measure width and height, how fullness works, and the 5 most common DIY mistakes β so your quotes compare apples to apples.
Updated: 2026-09-24
The three numbers you need
Each window needs just three numbers: frame width, height from the track position to where the curtain should end, and whether the track mounts above the frame or on the ceiling. With these, any shop can quote accurately.
Measuring width
- Drapes: measure the outer frame width and add 15-20cm per side so open curtains stack clear of the glass
- Roller / venetian blinds: measure the inner frame and add 5-10cm so light doesn't leak at the edges
- Bay and multi-pane windows: measure each pane's inner frame separately β never estimate from the total width
Measuring height
- Floor-length drapes: measure from the track position to the floor, leaving a 1-2cm gap so the hem doesn't drag
- Sill-length curtains: measure to 10-15cm below the sill
- Roller blinds: measure the inner frame height plus ~10cm overlap
Fullness ratios (fabric needed)
| Ratio | Look | Best for |
|---|---|---|
| 1.5Γ basic | Flat, sparse folds | roller blinds, sheers, small windows |
| 2Γ standard | Even, full folds | most drapes (recommended) |
| 2.5Γ luxurious | Deep, rich folds | heavy fabric, velvet, formal rooms |
The 5 most common mistakes
- Measuring the glass instead of the outer frame
- Not leaving swing clearance for inward-opening sashes
- Ignoring obstructions like sills, AC units and furniture
- Mixing feet and centimetres β state your unit when quoting
- Measuring one window per room β sizes vary even within the same flat
Got your numbers? Run them through the size calculator, or play Window Detective to learn per-window-type measuring tricks.
Sources: General measuring know-how; final sizes always come from the shop's on-site measure.