Hem Allowance Calculator
Find cut length from finished length, or calculate how much you can let out an existing hem.
Results are estimates. Always add extra for shrinkage, mistakes, and pattern matching.
How to Use the Hem Allowance Calculator
New Hem: Select a garment type for a suggested hem allowance, or choose a hem type and enter a custom amount. Enter your desired finished length to get the required cut length.
Let Out Existing Hem: Enter the current finished length and how deep the existing hem is. The calculator tells you the maximum length you can gain by letting out the hem.
Hem Allowance Guide by Garment Type
| Garment | Typical Hem | Fold Type | Notes |
|---|---|---|---|
| Shirt / Blouse | ½–1" | Double fold | Narrow for woven shirts |
| Dress | 1–2" | Single or double | Depends on skirt fullness |
| Pants / Trousers | 1.5–2" | Single fold | Wider for letting out later |
| Skirt | 1–2" | Single or double | Flared skirts: narrow hem |
| Curtains | 3–4" (double) | Double fold | Adds weight for drape |
Single vs. Double Fold
- Single fold: Fabric edge turned up once. Raw edge is hidden inside (use with serger or zigzag stitch).
- Double fold: Fabric edge turned up twice, enclosing the raw edge. Cleaner finish, uses more fabric.
About this Hem Allowance Calculator
This calculator answers two different questions: how long to cut a new garment piece so it ends up a specific finished length after hemming, and how much extra length you can gain by letting out an existing hem. For a new hem, cut length is simply the finished length plus the hem allowance for each fold — a double-fold hem uses the allowance twice, once per fold, which is easy to under-cut if you're not expecting it.
Letting out an old hem has a practical limit
The maximum you can gain is the current hem depth minus whatever seam allowance you need to keep for the new hem — but an old crease line, especially in wool or synthetic-blend fabric, can leave a visible shadow after being let out, even after pressing or steaming. Check how visible the old fold line is before counting on the full calculated gain. The garment-type presets are typical starting points, not fixed rules — always check your own pattern's stated hem allowance first. See the Seam Allowance Calculator for the seam side of the same math.