How to use the hem allowance calculator
- Choose inches or centimeters and enter the finished length you want.
- Enter the hem depth and choose a single turn or double turn hem.
- Enter the seam allowance at the top. Read the headline for the length to cut.
- In More options, enter the number of pieces and how many fit across the fabric width to find the fabric length to buy.
Formula
cut length = finished length + hem allowance + seam allowance
hem allowance = hem depth for a single turn, or 2 x hem depth for a double turn
fabric length = rows of pieces x cut length, with rows = pieces / pieces across, rounded up
Yards are inches divided by 36. Centimeters convert at 2.54 per inch. The seam allowance here is the one at the top edge. Add extra if you will also sew a seam at the bottom.
A 30 inch panel with a 2 inch hem
30 + 2 + 0.5 = 32.5 inches to cut, which is 82.55 centimeters. A double turn hem folds twice, so it uses 2 x 2 = 4 inches: 30 + 4 + 0.5 = 34.5 inches.
For five pieces cut two across the width, you need 3 rows (5 / 2 rounded up) of 32.5 inches, which is 97.5 inches or 2.708 yards. In centimeters, 60 + 2 + 1 = 63 cm, which is 24.8 inches.
Single and double turn hems
A single turn folds the raw edge up once and stitches it down, so the allowance equals the hem depth, and the raw edge is usually finished another way. A double turn folds the edge under before folding up, which hides the raw edge and uses twice the hem depth. Patterns say which one they assume, and many list the allowance on the pattern pieces already, so check before you add more.
Seam allowances vary by pattern, and the page lets you enter one value for the top edge. If the piece also has a bottom seam, add it to the finished length or the hem depth.
Buying enough fabric
Fabric is sold by length at a fixed width, so the number of pieces that fit across the width decides how long a cut you need. Allow extra for shrinkage if you will wash the fabric first, and for matching a pattern. See the Fabric Yardage Calculator, the Curtain Fabric Calculator and the Quilt Backing and Binding Calculator.
Assumptions and limits
- The finished length is the length after hemming. The hem and seam allowances are added to it.
- Pieces are straight and rectangular. Curved hems and tapered pieces need more care.
- Fabric width is recorded for reference. Check that the pieces fit across it with their widths and side seams.
- Shrinkage and pattern matching are not included.
Frequently asked questions
How much extra length do I add for a hem?
Add the hem depth to the finished length for a single turn, or twice the hem depth for a double turn, plus any seam allowance at the top. A 30 inch finished length with a 2 inch single hem and a half inch seam is cut at 32.5 inches.
What is the difference between a single and double hem?
A single turn folds the edge up once, using the hem depth. A double turn folds the edge under and then up, so it uses twice the depth and hides the raw edge. Choose the one your pattern calls for.
How do I work out the fabric to buy?
Divide the number of pieces by how many fit across the fabric width, round up to whole rows, and multiply by the cut length. Divide by 36 for yards. Five pieces, two across, at 32.5 inches is 97.5 inches, or 2.708 yards.
Does this include shrinkage?
No. If you will wash the fabric before sewing, buy extra to allow for shrinkage. How much depends on the fabric, so check the label or wash a small sample first and measure it.