Fabric width converter
When a pattern specifies a length at one fabric width and your fabric is a different width, multiply the pattern length by the pattern width and divide by your width: 3 metres of 115 cm fabric becomes 2.3 metres of 150 cm fabric. This is an area equivalence, and it holds only for plain, non-directional fabric whose pattern pieces can be rearranged freely. A one-way design, a nap, or any single piece wider than the narrower roll breaks it — the converter below flags those cases rather than printing a figure you cannot rely on.
What your pattern says, and what you have
2.3 m
The area works out at 2.3 m, rounded up to nearest 10 cm.
- Exact area equivalent
- 2.3 m
- Change in width
- 115 → 150 cmwider
The area conversion assumes every piece still fits across the new width. Measure the widest piece on your pattern and enter it, and this becomes a check rather than an assumption.
How we got this
- Area of fabric the pattern needs — 3.45 m²3 m × 115 cm
- Same area at the new width — 2.3 m3 m × 115 cm ÷ 150 cm
- Buy, rounded up (nearest 10 cm) — 2.3 m2.3 m rounded up
How this works
The pattern tells you an area of cloth, expressed as a length at a particular width. Keep the area and change the width, and the length follows:
new length = pattern length × pattern width ÷ your width
| Step | Working | Result |
|---|---|---|
| Area of fabric the pattern needs | 3 m × 115 cm | 3.45 m² |
| Same area at the new width | 3 m × 115 cm ÷ 150 cm | 2.3 m |
| Buy, rounded up (nearest 10 cm) | 2.3 m rounded up | 2.3 m |
When the area conversion is wrong
Area equivalence assumes the pattern pieces can be rearranged freely to fill whatever shape the new roll gives you. Fabric does not always allow that, and three situations break it outright:
- A piece wider than the roll. If any single pattern piece is wider than your fabric, no length rescues it — the piece will not fit. This is why the converter asks for your widest piece, and refuses to give a confident answer without it. To see how a specific set of pieces actually lands on a roll, use the fabric yardage calculator.
- A directional print or a nap. Velvet, corduroy, a one-way floral: pieces cannot be rotated to nest together, so the same area no longer lays out in the same length. Add at least one extra pattern-piece length.
- Going narrower. Two pieces that used to sit side by side on a 150 cm roll may not both fit on a 115 cm one, and the leftover strip down the side is waste the area maths does not know about.
The converter flags each of these on the result rather than in a footnote. Where the maths cannot be trusted it says so, because a confident wrong number here costs a whole project.
What roll widths actually measure
The trade uses imperial and metric labels for the same cloth, and rounds both. They are not equivalent, and the gap is large enough to matter when you are joining widths to reach a fixed finished size.
| Sold as | Also labelled | Exact | Label error | Typical use |
|---|---|---|---|---|
| 36 in | 90 cm | 91.44 cm | -1.44 cm | Quilting cottons, older dress fabrics |
| 44 in | 112 cm | 111.76 cm | 0.24 cm | Standard quilting cotton |
| 45 in | 115 cm | 114.3 cm | 0.7 cm | Dressmaking cottons, commercial patterns |
| 54 in | 137 cm | 137.16 cm | -0.16 cm | Upholstery, curtain lining |
| 55 in | 140 cm | 139.7 cm | 0.3 cm | Curtain and furnishing fabrics |
| 60 in | 150 cm | 152.4 cm | -2.4 cm | Knits, wide dress fabrics |
| 108 in | 274 cm | 274.32 cm | -0.32 cm | Wide-back quilting fabric |
54 inches is 137.16 cm, not 140. The two get used interchangeably for furnishing fabric and they are nearly 3 cm apart. Over four joined widths that is more than a centimetre of finished width per seam — enough to leave a made-to-measure curtain visibly narrow. The curtain fabric calculator works in the width you enter for exactly this reason.
Roll widths are nominal in a second way too: the figure on the label usually includes the selvedge, which is not usable. If the width matters, measure the fabric rather than trusting the bolt end, and enter what you measured.
A rule of thumb worth knowing
Going from 115 cm to 150 cm cuts the length you need by about a quarter. Going from 150 cm back to 115 cm adds about a third — not a quarter, because the ratio is not symmetric. People routinely convert one way with the right factor and the other way with the same factor, and end up short. The converter above does the arithmetic in whichever direction you enter it.
Common questions
- Is 54 inches the same as 140 cm?
- No. 54 inches is 137.16 cm, not 140. The trade uses the two labels interchangeably for furnishing fabric, but they are nearly 3 cm apart — enough to matter when you are joining widths to a fixed finished size.
- When does the conversion stop working?
- When the pieces cannot be rearranged. If any single pattern piece is wider than the narrower roll it simply will not fit at any length. A directional print or a fabric with a nap also breaks it, because pieces can no longer be rotated to nest together.
- Should I add extra on top of the converted figure?
- Yes, when going to a narrower fabric. The area maths assumes pieces that used to sit side by side still do, and on a narrower roll they often cannot — so the honest answer is the converted figure plus one extra pattern-piece length as insurance.
Related tools
Curtain fabric calculator
Track width, drop, fullness and pattern repeat in; metres or yards to buy out, with every allowance adjustable.
Fabric yardage calculator
Piece size, how many, roll width — the length to buy, and the strip you pay for but never cut.
Fabric GSM calculator
g/m², oz/yd², running-yard ounces and momme — plus the weight of an unlabelled fabric from a swatch.
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.
Yards to metres
Convert a pattern written in yards to metres, with the common cut lengths tabulated.