Curtain Fabric Calculator
Work out how much fabric you need for curtains. Enter your track width, finished drop, fabric width, fullness ratio and pattern repeat to get the number of widths, cut length per width and total yardage or metres.
Estimate Fabric Yardage for Your Curtains
Curtain Fabric Formula
Where:
- \(W\) — window / curtain track width (cm or in)
- \(R\) — fullness ratio (how much wider the curtain is than the track)
- \(F\) — usable width of one bolt of fabric
- \(n\) — number of fabric widths needed
- \(D\) — finished drop of the curtain
- \(H_1\) — heading allowance (fabric for the header and top turn)
- \(H_2\) — bottom hem allowance
- \(P\) — vertical pattern repeat (0 for plain fabric)
- \(L_{cut}\) — cut length of each width
- \(L_{total}\) — total fabric length to buy
The first line works out how many fabric widths must be joined side by side so the curtain is wide enough to gather into folds. The next lines add the heading and hem allowances to the drop, rounding up to a whole pattern repeat if the fabric is patterned. The final line multiplies the number of widths by the cut length.
Curtain Fabric – Calculation Example
Example: a curtain track is 150 cm wide, the finished drop is 200 cm, the fabric is 140 cm wide, fullness is 2× (pencil pleat), with a 10 cm heading allowance, a 15 cm hem allowance and plain fabric (pattern repeat 0).
\[
W \times R = 150 \times 2 = 300 \text{ cm of flat fabric} \\
n = \left\lceil \frac{300}{140} \right\rceil = 3 \text{ widths} \\
L_{cut} = 200 + 10 + 15 = 225 \text{ cm} \\
L_{total} = 3 \times 225 = 675 \text{ cm} = 6.75 \text{ m} \approx 7.38 \text{ yd}
\]
Result: 3 widths, each cut 225 cm (88.6 in) long, for a total of 6.75 m (7.38 yards) of fabric.
If the same fabric had a 32 cm pattern repeat, each cut length would be rounded up from 225 cm to \(8 \times 32 = 256\) cm so the pattern matches at the seams, giving \(3 \times 256 = 768\) cm — 7.68 m in total.
How to Use the Calculator
- Enter the Window / curtain track width — the length of the track or pole, not the glass — and pick cm or in.
- Enter the Finished drop: the curtain length from the heading (where it hangs from the track or pole) down to the hem.
- Fill in the Fabric width — the usable width of one bolt, edge to edge. Most furnishing fabrics are 137–150 cm (54–59 in) wide.
- Choose a Fullness ratio: 2× is standard for pencil-pleat headings, 1.5× suits eyelet or tab-top styles, and 2.5× or 3× give deeper, more luxurious folds.
- Enter the Heading allowance and Bottom hem allowance. A double 5 cm hem needs 10 cm, for example. Set either to 0 if your drop already includes it.
- Enter the Pattern repeat — the vertical distance before a printed pattern repeats — or leave 0 for plain fabric.
- Read the results: the number of fabric widths needed, the cut length per width in cm and inches, and the total fabric length in metres and yards.
What the Calculation Means
Curtains are never cut exactly the width of the window. They are made wider — typically twice the track width — so the fabric gathers into soft folds when the curtain is drawn. This extra fabric is called fullness. A 150 cm track with 2× fullness needs 300 cm of flat fabric, which usually means joining two or more lengths (widths) of fabric side by side.
Each of those widths must be cut long enough for the finished drop plus the fabric that is hidden in construction: a heading allowance at the top to form the header and turn under, and a hem allowance at the bottom. That is why the cut length is always longer than the drop you measure at the window.
If the fabric has a printed pattern, adjacent widths must start at the same point in the pattern or the design will visibly break at each seam. To guarantee this, each cut length is rounded up to a whole multiple of the pattern repeat. The larger the repeat, the more extra fabric this can add — a 200 cm drop with a 64 cm repeat, for instance, forces each cut up to 256 cm.
The final figure — number of widths times cut length — is the total length of fabric you need to buy. Fabric is sold by the metre or yard off a roll of the width you entered, so this total, not the window size, is what you take to the shop.
Assumptions, Limitations and Practical Tips
- Usable width matters. Bolts often have a selvedge or printing border that can't be used, so usable width can be several cm less than the stated width. Enter the usable figure — a smaller width may add a whole extra width to the estimate.
- Buy a little extra. Round up when ordering and consider one extra width's worth of fabric as a safety margin for shrinkage, seam matching mistakes, or future repairs.
- Rail-mounted curtains need less fullness on an eyelet or tab-top heading (1.5× is common) because the folds are spaced by the rings, whereas a pencil-pleat tape gathered with hooks looks best at 2×–2.5×.
- Lined curtains need the same amount of lining fabric; the calculator covers the face fabric only.
- Directional and large patterns (stripes, damasks, one-way designs) may force every width to start at the same repeat point; this calculator handles the standard vertical repeat, but very large repeats or half-drop patterns can need additional fabric — check with your supplier.
- Pre-shrink where appropriate. Some natural fabrics shrink when dry-cleaned; if in doubt, allow extra length or pre-treat the fabric before cutting.
Frequently Asked Questions
How do I calculate curtain fabric by hand without a calculator?
Multiply the track width by the fullness ratio, divide by the fabric width, and round up to get the number of widths: \( n = \lceil W \times R / F \rceil \). Then add your heading and hem allowances to the finished drop to get the cut length per width, rounding up to a whole pattern repeat if needed. Multiply the two figures together for total yardage. Always round up, never down — short fabric can't be stretched.
What fullness ratio should I use for my curtain style?
Use 2× for pencil pleat (the most common choice), 2.5× for fuller, deeper folds, and 3× for luxurious gathers or sheer fabrics that need volume to look good. Eyelet (grommet) and tab-top curtains work best at 1.5×–2× because the rings space the folds evenly, and too much fabric makes the waves bulge. Cartridge and French pleat headings look best at 2×–2.5×.
How many metres of fabric is a yard, and how do I convert?
One yard equals 0.9144 metres, or about 91.44 cm — roughly 10% more than a metre. To convert metres to yards, divide by 0.9144; to go the other way, multiply by it. A 6.75 m estimate is about 7.38 yards. If a shop sells by the yard but you measured in cm, convert the total once at the end rather than converting each measurement, to avoid rounding errors stacking up.
Why should I measure the track or pole, not the window glass?
Curtains hang from the track or pole, so that's the width they must cover when drawn. The track is usually wider than the glass so curtains can stack clear of the window and block light at the edges. If you measure only the glass, your curtains will be too narrow to meet in the middle or cover the returns. If you haven't bought the track yet, plan it 15–20 cm beyond the window on each side.
How much extra fabric should I buy beyond the calculator's estimate?
Add one extra width's worth of fabric — the cut length figure — as a safety margin. This covers cutting errors, seams that need repositioning to match a pattern, shrinkage in natural fibres like linen and cotton, and future repairs. Fabric dye lots vary, so matching a bolt bought later can be impossible. For plain fabric with no repeat, a smaller buffer of 10–20 cm per width may be enough.
Does this calculator include lining and interlining fabric?
No — the estimate covers the face (decorative) fabric only. Lining is usually cut to the same number of widths and a similar length, so a plain lining typically needs about the same total metreage, though it doesn't require pattern matching. Interlining (bump or sarille) adds warmth and body but also adds bulk at the seams. Budget for lining separately, and remember blackouts and interlinings are sold in their own roll widths, often 150 cm or wider.
What is a half-drop pattern repeat, and does the calculator handle it?
A half-drop repeat offsets the pattern by half its height on alternating widths, so adjacent panels match at a point shifted by half a repeat. This calculator assumes a standard straight match, so half-drop fabrics need extra fabric — often up to an extra half repeat per width. Railroading (turning the fabric 90° so the print runs sideways) can save fabric on some designs but only works with non-directional patterns. Ask your supplier before cutting.