Curtain Fabric Calculator
Extra fullness is often free, because widths round up. And a 36in pattern repeat can waste less fabric than a 24in one.
The working
Extra fullness is often free
Curtains are gathered, so the fabric has to be a multiple of the track width — not the track width itself. But you cannot join two thirds of a width, so the number of widths is a ceiling, and that makes fullness free in bands. On a 60″ track with 54″ fabric:
| Fullness | Fabric needed | Widths | |
|---|---|---|---|
| 1.5× | 90″ | 2 | you could have 1.73× for the same money |
| 2× | 120″ | 3 | you could have 2.60× for the same money |
| 2.25× | 135″ | 3 | you could have 2.60× for the same money |
| 2.5× | 150″ | 3 | you could have 2.60× for the same money |
| 2.75× | 165″ | 4 | you could have 3.47× for the same money |
| 3× | 180″ | 4 | you could have 3.47× for the same money |
Two, two and a quarter and two and a half all cost exactly the same fabric. If you were planning 2×, you can have 2.5× for nothing — and if you were planning 2.75×, dropping back to 2.5× saves an entire width. The calculator above tells you which side of a boundary you are on.
A bigger repeat is not always more wasteful
Every drop has to start at the same point in the pattern, so each cut length rounds up to a whole number of repeats. The obvious guess is that a bigger repeat wastes more. It does not — on a 106″ cut:
| Repeat | Cut becomes | Wasted per drop |
|---|---|---|
| plain | 106″ | 0″ |
| 6″ | 108″ | 2″ |
| 12″ | 108″ | 2″ |
| 18″ | 108″ | 2″ |
| 24″ | 120″ | 14″ |
| 36″ | 108″ | 2″ |
The 36″ repeat costs 2″ and the 24″ repeat costs 14″. The waste is not the size of the repeat — it is
waste = (−cut) mod repeat
which depends entirely on where your cut length happens to fall between multiples. A 24″ repeat on a 106″ cut lands just past a boundary and pays for nearly a whole extra repeat; a 36″ repeat lands just under one and pays almost nothing. Across ordinary cut lengths and repeat sizes, a bigger repeat wastes less about a quarter of the time.
Which means the hem depth is a lever. Changing it by an inch or two moves the cut length across a boundary and can save a foot of fabric on every drop. Try it in the box above before you buy.
Cushions, tablecloths and bunting
Never put a seam down the middle of a tablecloth. When the cloth is wider than the fabric, the join is the thing everyone looks at, and the centre of a laid table is exactly where it will be seen. Use a full-width centre panel with narrower panels seamed either side of it. It costs the same fabric and reads as deliberate rather than economical.
Bunting flags are cut in pairs. Each flag is two triangles sewn right sides together and turned, so the fabric is double what the flag count suggests — the single most common underestimate in the whole business. Cutting them alternately point-up and point-down nests them and roughly halves the waste.
Before you cut
- Measure the track, not the window. A track usually extends well beyond the frame so the curtains can stack clear of the glass.
- Measure the drop from the track, not the top of the curtain. Where the hooks sit relative to the heading changes the finished length.
- Buy one extra repeat if the pattern is large and the fabric is discontinued-risky. Matching a fifth drop later is not possible without it.
- Hang and let them drop before hemming. Long curtains lengthen under their own weight over a week or two, especially in linen.
- Line them. Lining doubles the fabric bill and roughly trebles the life of the curtain, because sunlight is what destroys them.
How to use
- Measure the track, not the window, and the drop from the track.
- Check whether more fullness costs anything before settling for less.
- Try changing the hem depth — it can move you across a repeat boundary.
- Hang them for a fortnight before hemming.
Frequently asked questions
How much fabric do I need for curtains?
Multiply the track width by the fullness your heading needs — about 2 for standard gathered tape, 2.5 for pencil pleat, 3 for goblet — then divide by the usable fabric width and round UP to a whole number of widths. Multiply that by the cut length, which is the drop plus the heading allowance plus the hem.
What fullness do curtains need?
Two times the track width is the usual minimum; below that a curtain reads as a flat panel rather than a curtain. Pencil pleat is normally 2.5, goblet and pinch pleats up to 3, and tab tops or eyelets can work at 1.5 because they are meant to hang in soft waves rather than pleats.
Is more fullness always more fabric?
No, and this is worth checking before you compromise. Because you cannot join part of a width, the number of widths is a ceiling — so on a 60 inch track with 54 inch fabric, 2, 2.25 and 2.5 times fullness all cost exactly three widths. If you were planning 2, you can have 2.5 for nothing.
How much extra fabric does a pattern repeat need?
Every drop has to start at the same point in the pattern, so each cut length rounds up to a whole number of repeats. How much that costs depends entirely on where your cut length falls between multiples — it is the remainder, not the repeat size.
Does a bigger repeat always waste more?
No, and the assumption catches people out. On a 106 inch cut, a 36 inch repeat wastes 2 inches while a 24 inch repeat wastes 14. The waste is the negative of the cut length modulo the repeat, so a big repeat that lands just under a multiple costs almost nothing while a smaller one just past a boundary pays for nearly a whole extra repeat.
Can I reduce the repeat waste?
Often, yes. Changing the hem depth by an inch or two moves the cut length across a repeat boundary and can save a foot of fabric on every drop. It costs nothing to try before you buy, and on a four-width curtain in an expensive fabric it is worth real money.
Should I measure the window or the track?
The track. It usually extends well beyond the window frame so the curtains can stack clear of the glass when open, and that extra width is fabric you have to buy. Measure the drop from the track as well, not from the top of the curtain, because where the hooks sit changes the finished length.
How deep should a curtain hem be?
Around 4 inches doubled, so 8 inches of fabric, for a full-length curtain. A deep hem adds weight, which makes the curtain hang straight instead of kicking out at the bottom. Short curtains can take less, and a very lightweight fabric wants more weight rather than less.
Why should I let curtains hang before hemming?
Because long curtains lengthen under their own weight over a week or two, especially in linen and especially if they were made in a warm dry room and hung in a cold damp one. Hang them, leave them a fortnight, then mark the hem from the floor up.
Is lining worth it?
Almost always. Lining roughly doubles the fabric bill and roughly trebles the life of the curtain, because sunlight is what destroys curtains and the lining takes it instead. It also improves how they hang, insulates the window, and stops the outside world seeing the colour of your living room at night.
How much fabric for cushion covers?
Two panels per cushion, each cut to the pad size plus seam allowance, and work out how many fit across the usable fabric width. Small panels nest well so this is the forgiving calculation. Buy the pad slightly larger than the cover — that is what makes a cushion look plump rather than half-empty.
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