Curtain calculator
Work out how much curtain fabric to buy from the track or pole width, the drop and the fullness of your heading, with pattern repeats. Or see the minimum ready-made curtain width that will look full when closed.
Track and drop
Heading and fabric
About the curtain calculator
Work out how much curtain fabric to buy from the track or pole width, the drop and the fullness of your heading, with pattern repeats. Or see the minimum ready-made curtain width that will look full when closed.
Part of SmartCalcy’s home & construction tools. It runs in your browser with no account, uses your own currency and units (change them at the top of the page), and gives estimates for information only, so check official guidance before you rely on a result.
How to use the curtain calculator
What it calculates and when to use it
Works out curtain fabric, the number of fabric widths and the cut length of each drop from your track or pole, drop and heading fullness, or the minimum ready-made curtain size to buy.
How to use it, step by step
- Measure the track or pole between the end stops.
- Measure the drop from the top of the track to the hem position.
- Choose the fullness for your heading.
- Enter the fabric width, hem allowance and any pattern repeat.
What each input means
- Track width – Starts at 150 cm.
- Overlap and returns – Starts at 20 cm.
- Finished drop – Starts at 220 cm.
- Fullness – 2× for pencil pleat and eyelet, 2.2× for wave, 2.5× for pinch pleat.
- Fabric width – Starts at 137 cm.
- Hem and heading – Starts at 30 cm.
- Pattern repeat – 0 for plain fabric.
How to read the results
- Fabric to buy – Total length, with the widths and cut drop.
- Ready-made size – Minimum flat width of each curtain.
- How it adds up – Flat width, widths per curtain and the cut drop.
The formula
Flat width = (track + overlap) × fullness. Widths = flat width ÷ fabric width, rounded up (and to an even number for a pair). Cut drop = drop + allowance, rounded up to whole pattern repeats. Fabric = widths × cut drop.
A worked example
With the starting entries: (150 + 20) × 2 = 340 cm flat; 340 ÷ 137 = 2.48, so 3 widths, made 4 for a pair; 4 × 250 cm = 10 m of fabric. Ready-made: two curtains at least 170 cm wide.
Assumptions and limits
- Allowances vary with the heading tape; check your pattern.
- Pattern matching across widths may need extra fabric.
Common mistakes
- Measuring the window instead of the track.
- Ignoring the pattern repeat.
- Buying ready-made curtains only as wide as the track.
Frequently asked questions
How wide should curtains be?
Usually 2 to 2.5 times the track width in flat fabric, depending on the heading.
How much extra for hems?
About 30 cm (12 in) per drop is common for hem and heading together.
How do I measure the drop?
From the top of the track, or the bottom of the pole rings, to where the curtain should end.
Related tools
Buying ready-made instead?
- Look for
- 2 curtains at least 170 cm wideflat, ungathered width
- Drop
- 220 cm
How it adds up
- Flat width needed
- 340 cm(150 + 20) × 2
- Widths of fabric
- 4made even for a pair
- Widths in each curtain
- 2
- Cut drop
- 250 cm220 + 30 allowance