Fabric maths you can check
Every calculator here shows the arithmetic behind its answer and lets you change every allowance it used. Two fabric calculators can disagree and both be right, because curtain making has no single standard — so the useful thing is not another number, it is a number you can see the reasoning for.
Fabric Calculators
Work out how much fabric a project needs — curtains, upholstery, cushions, tablecloths and blinds — with every allowance visible and adjustable.
Curtain fabric calculator
Track width, drop, fullness and pattern repeat in; metres or yards to buy out, with every allowance adjustable.
Curtain fullness calculator
How many widths each curtain needs at the fullness you want — and what whole widths really gather to.
Pattern repeat calculator
The cut length a repeat forces, what is trimmed from every piece, and what matching the design costs.
Fabric yardage calculator
Piece size, how many, roll width — the length to buy, and the strip you pay for but never cut.
Cushion fabric calculator
Cover size, back opening and piping in; the length to buy and a row-by-row cutting plan out.
Upholstery fabric calculator
An editable panel list instead of a rule of thumb — with the cutting plan and the seams it implies.
Seam allowance calculator
Finished size to cut size — and what a different allowance does to the garment you end up with.
Curtain lining calculator
Lining on its own narrower roll, from the flat width your curtains already need.
Roman blind fabric calculator
Fabric and lining for a flat blind — no fullness, but the repeat still decides the cut.
Curtain heading tape calculator
Tape, hooks and cord for a pair of curtains — and why hooks are not counted on the tape.
Tablecloth fabric calculator
Table plus drop, round or rectangular — and whether turning the cloth loses a seam.
Bias binding calculator
Straight-grain strips or one continuous bias strip from a square, costed side by side.
Fabric Conversions
Convert between yards and metres, inches and centimetres, and between bolt widths, using the exact definitions rather than the trade approximations.
Yards to metres
Convert a pattern written in yards to metres, with the common cut lengths tabulated.
Metres to yards
Convert metres to yards and to the eighth-yard increments a US cutting counter uses.
Fabric width converter
Pattern written for one bolt width, fabric bought at another — work out the equivalent length.
Fabric GSM calculator
g/m², oz/yd², running-yard ounces and momme — plus the weight of an unlabelled fabric from a swatch.
Reference Charts
The figures the calculators use, laid out as tables — ready-made curtain sizes, roll widths, seam allowances and fabric weights.
Standard curtain sizes
Ready-made drops and widths, in both systems — and what each width really gathers to.
Fabric width chart
Standard roll widths in both systems, and the gap between the label and the cloth.
Seam allowance chart
Every common allowance in millimetres and inches, and which projects use which.
Fabric weight chart
Weight bands in g/m² and oz/yd², and what each band is actually used for.
Upholstery yardage chart
What the trade charts quote, why they disagree by 80%, and what a piece list gives instead.
Curtain heading types
Five headings compared on fullness, allowance and what they cost in cloth.
Why this site exists
Search for a curtain fabric calculator and you will find a dozen. Enter the same window into three of them and you will get three answers, none of which explains itself. One assumed a 15 cm heading allowance, one assumed 25 cm, and the third quietly rounded your fullness up. There is no way to tell which, so there is no way to decide which to trust.
The fix is not more accuracy — it is showing the working. Every figure printed on these pages, including the worked examples in the supporting text, is produced by the same code the calculator runs, and the derivation is on the page. Where a calculation rests on an assumption a professional would argue with, the assumption is written down and left editable. Where the maths does not hold at all, the tool says so instead of printing a confident number.
Read the methodology for the formulas and the full assumption list.