What this calculator does
Curtain fabric needed works out fabric width and panel count for curtains, from window size and desired fullness. Enter your own figures above and the answer updates as you type: nothing is fixed in the code, so the result reflects exactly the numbers you supply.
The formula this calculator evaluates is printed under the tool and explained below, so you can check the working by hand or reuse it in a spreadsheet.
The formula
FormulaTotal fabric width = window width × fullness ratio; panels = total fabric width ÷ fabric width per panel; drop length = window/rod height + hem + heading allowance
The inputs explained
| Field | What to enter |
|---|---|
| Rod / window width (cm) | A number, measured in cm. Starts at 150. |
| Fullness ratio | A number. Starts at 2. |
| Fabric width per panel (bolt width) (cm) | A number, measured in cm. Starts at 137. |
| Finished drop (rod to floor/sill) (cm) | A number, measured in cm. Starts at 200. |
| Hem allowance (top + bottom) (cm) | A number, measured in cm. Starts at 20. |
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How the answer changes with rod / window width
Every other input is held at the calculator’s starting values while rod / window width varies. Select any row to load that scenario into the calculator.