How to use it
- Measure the Window width and the Height of the rod above the floor.
- Choose the Heading, then type the Rod overhang on each side and the Gap above the floor.
- Type the Width of the fabric as sold and the Hem and heading allowance.
- Read the Fabric widths, the Cut length of each width and the Fabric to buy.
How the fabric is worked out
The rod is wider than the window, by the overhang on each side, so the curtains can be drawn back clear of the glass. The fabric must be gathered to a fraction of the rod width, the fullness, so each curtain is many times the rod width. A rod pocket is gathered to about 2 times, an eyelet to about 1.5 times, and a pleated heading to about 2.5 times.
The fabric is then cut into widths, each as long as the drop plus the allowance for the hem and heading. The widths are rounded up, so a fabric that is only just short needs a whole extra width.
rod width = window width + 2 × overhang
fabric across = rod width × fullness (rod pocket 2, eyelet 1.5, pleated 2.5)
widths = fabric across ÷ fabric width, rounded up
cut = (rod height − floor gap) + hem and heading allowance
fabric to buy = widths × cutThe fullness figures
The Hues, a curtain guide, gives 2 to 2.5 times for a rod pocket and 1.5 to 2 times for an eyelet heading. This page uses the lower figure of each range.
The pleated figure of 2.5 times is the usual value for a pinch-pleat heading. It is not confirmed from a curtain maker's sheet here, so check the heading tape's own spacing and fullness.
What this calculator does not include
- Lining, interlining and the pattern repeat of a printed fabric, which can add a whole drop to each width.
- Curtains that pair with blinds, a stack allowance on the floor, and the tracks, rails and brackets.
- Shrinkage of the fabric on the first wash, which the fabric's own label or the maker states.
Worked example: a 150 cm window, rod pocket, 140 cm fabric
With 15 cm overhang on each side the rod is 150 + 2 × 15 = 180 cm. Two times the rod is 360 cm of fabric, which needs 360 ÷ 140 = 2.57, so 3 widths.
The drop is 240 − 1 = 239 cm and the cut length is 239 + 15 = 254 cm. Three widths of 254 cm is 7.62 m of fabric.
| Rod pocket | Pleated | Eyelet | |
|---|---|---|---|
| Fabric across the rod | 360 cm | 450 cm | 270 cm |
| Widths of 140 cm | 3 | 4 | 2 |
| Fabric to buy (254 cm cut) | 7.62 m | 10.16 m | 5.08 m |
Frequently asked questions
How much fabric do I need for curtains?
Multiply the rod width by the fullness of the heading, divide by the fabric width and round up to get the number of widths. Multiply that by the cut drop. A 150 cm window with a rod pocket heading needs about 7.6 m of 140 cm fabric.
What is fullness?
The number of times the rod width the fabric is gathered to. More fullness gives a richer, fuller curtain that folds more; less fullness gives a flatter look and uses less fabric.
Why is the rod wider than the window?
So that the curtains can be drawn back clear of the glass and let in as much light as possible. A rod that runs about 15 cm past each side of the window is a common choice.
Why do I need an allowance for the hem and the heading?
The hem at the bottom and the heading at the top are folded over, so the cut fabric must be longer than the finished drop. The allowance is the total added to the drop.
Does the tool store what I enter?
No. The calculation runs in your browser and nothing you type is sent to us or stored.
Sources
Figures and text last checked on Tuesday, November 10, 2026.