How this calculator works
The number of pieces across the fabric is the fabric width divided by the piece width, rounded down. The number of rows is the number of pieces you need divided by the pieces across, rounded up, because a partial row still takes the full length of the row. Multiply the rows by the piece length for the fabric to buy. The waste figure compares the area of the pieces with the area of the fabric piece, so it explains why the last row often looks expensive.
Formula
pieces across = fabric width / piece width, rounded down. rows = pieces needed / pieces across, rounded up. fabric length = rows x piece length. waste = 1 - (pieces x piece width x piece length) / (fabric length x fabric width).
Worked example
On fabric 150 cm wide, pieces 40 cm wide fit 3 across. Twenty pieces need 20 / 3 = 6.67 rows, rounded up to 7, so the fabric length is 7 x 50 = 350 cm, or 3.5 m. That gives 21 pieces, so one is spare, and the waste share is 1 - (20 x 40 x 50) / (350 x 150) = 23.8 percent.
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Frequently asked questions
Should I add seam allowance to the piece size?
Yes. Enter the size of the piece after adding seam and hem allowances, because that is what you cut. If you enter the finished size, the fabric will be short by the allowances on every edge.
Can I rotate some pieces to fit better?
You can if the fabric has no directional print or nap. Rotating pieces changes the calculation and can reduce waste on non-directional fabric, but the simplest nesting is the one this page uses: all pieces in the same orientation.
Why is the waste so high?
The last row is often partly empty, and offcuts beside the pieces may be too narrow to use. The waste figure includes both. With small pieces and a wide fabric, fitting more across reduces the number of rows and the waste.
Does the fabric width include the selvedge?
Use the usable width after cutting off the selvedge, usually 1 to 2 cm on each side. The selvedge is woven differently and is not suitable for most pieces.