Hem Allowance Calculator for Cut Length
Before you cut fabric you need to add extra length for the hem and the seam, or the finished piece ends up short. This calculator takes the finished length you want, adds a hem allowance at one end and a seam allowance at the other, and returns the length to cut. Tick double fold to turn the raw edge under twice, which uses double the hem allowance for a clean enclosed edge.
How to add hem allowance
- Enter the finished length you want the piece to be, in inches.
- Set the hem allowance for the hemmed end.
- Tick Double fold hem if the raw edge turns under twice, which doubles the hem used.
- Set the seam allowance for the other end, or tap a 1/4, 1/2 or 5/8 inch preset button.
- Read the Total allowance and Cut length cards, then click Copy length.
Examples
28 inch finished, 2 inch single hem, 5/8 inch seam
Finished 28 in, hem 2 in, seam 0.625 in, single fold
Total allowance 2.625 in, cut length 30.625 in
40 inch curtain panel with a double fold hem
Finished 40 in, hem 2 in, seam 0.5 in, double fold
Hem used 4 in, total allowance 4.5 in, cut length 44.5 in
30 inch piece with a narrow quarter inch seam
Finished 30 in, hem 1 in, seam 0.25 in, single fold
Total allowance 1.25 in, cut length 31.25 in
Frequently asked questions
What is a double fold hem?
A double fold hem turns the raw edge under twice so no raw fabric shows on the inside. Because the fabric folds up twice, it uses double the hem allowance. Ticking the box changes a 2 inch hem into 4 inches of fabric used.
How much hem allowance should I add?
Around 1 inch suits light hems, while 2 to 3 inches gives trousers, skirts and curtains a weightier drape. Wider hems hang better on heavy fabric. When in doubt add a little extra, since you can always trim but you cannot add length back.
Why is 5/8 inch the default seam allowance?
Most commercial garment patterns use a 5/8 inch, which is 0.625 inch, seam allowance as the industry standard. The preset buttons let you switch to 1/4 inch for quilting or 1/2 inch for many home and craft projects with one tap.
How is the cut length worked out?
The hem used is doubled when double fold is ticked, then added to the seam allowance to give the total allowance. The cut length is your finished length plus that total. For a 28 inch piece with a 2 inch hem and 5/8 inch seam that is 30.625 inches.
Does this cover both ends of the piece?
It adds one hem at one end and one seam allowance at the other, which fits most panels and garment pieces. If both ends are hemmed, enter your second hem amount in the seam allowance field so both folds are counted.
What units does it use?
All fields are in inches. To work in centimetres convert first, for example a 1 inch hem is 2.54 cm, then read the cut length back in inches and convert the result. The math is the same in any unit.
Can I enter fractions like 5/8?
Enter fractions as decimals: 5/8 becomes 0.625, 1/2 becomes 0.5 and 1/4 becomes 0.25. The seam preset buttons fill these common values for you, and results are rounded to four decimal places.
Does it account for shrinkage or seam take-up?
No. It adds only the hem and seam you specify. If your fabric shrinks, pre-wash it before cutting, or add a small extra margin to the finished length so the piece stays true after laundering.
Is anything I enter sent to a server?
No. The calculation runs in your browser and none of your measurements leave your device, so your project details stay private.
Learn more
- Single vs double fold hems and how much fabric each needs
How single and double fold hems differ, why the double fold uses twice the allowance, and how to pick the right depth for your fabric.
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