Hem Allowance Calculator
Compute the total fabric cut length for a garment or curtain panel with a chosen hem depth, hem style and top seam allowance, so the finished length matches the design. Useful for skirts, trousers, curtains, and any project where precise length matters.
Last updated: September 2026
Total Cutting Length
38.13 inches
Formula below · 4 sources (sewmag.co.uk, lovecrafts.com, threadsmagazine.com, engineerfix.com) · Updated Sep 2026
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About this calculator
When cutting fabric, the cut length must exceed the finished length to accommodate the hem fold at the bottom and the seam allowance at the top where the piece attaches to a waistband, header, or yoke. The formula is cutLength = finishedLength + hemDepth + turnUnder + topSeamAllowance, where finishedLength is the desired visible length of the finished piece, hemDepth is the visible depth of the hem (how far up from the bottom edge the hem appears, e.g. 1 inch for a standard hem), and topSeamAllowance is the seam allowance at the top edge (typically 5/8″ = 0.625″ or 1/2″ = 0.5″). For a garment double-fold hem the raw edge is first turned under by a small amount to hide it, and the calculator uses 1/2 inch for that turn-under (1/4–1/2 inch is usual); the hem is then folded up by its full depth, so the hem uses depth + 1/2 inch of fabric. A curtain double hem is different: the fabric is folded up by the full hem depth twice, so the hem uses 2 × depth (a 3-inch curtain hem needs 6 inches) and the doubled layer adds weight that helps the curtain hang straight. Pick the matching hem style. Edge cases: for blind hems, bias-tape-bound hems or rolled hems the math differs slightly (rolled hems need only 1/4–1/2 inch extra). Curved hems (circle skirts, peplums, shaped trousers) need a shallower hem because the curved fabric must turn under flat — typically 1/2 inch max for circle skirts versus 2 inches for a straight skirt. Knits don't unravel and can use a small single-fold hem (1/2 inch) with a stretch stitch. The formula does not include shrinkage; pre-wash natural fibers before measuring and add 3–8% extra length for fabrics that shrink in laundering.
How to use
Example 1 — straight skirt. Finished length 24 inches (mid-knee), 1-inch garment double-fold hem, 5/8-inch waist seam allowance. Step 1: cutLength = 24 + 1 + 0.5 + 0.625 = 26.125 inches. Step 2: cut the fabric panel at 26.125 inches (26 1/8″). After sewing the waistband seam (5/8″), turning the raw edge under (1/2″) and folding up the 1-inch hem, the finished skirt measures 24 inches. Verify: 26.125 − 1 − 0.5 − 0.625 = 24 ✓. Example 2 — deep curtain hem. Finished curtain length 84 inches (floor length), 3-inch curtain double hem (the fabric is folded up 3 inches twice; curtains hang better with weight at the bottom), 1.5-inch rod pocket header (treated as the 'top seam allowance'). Step 1: cutLength = 84 + 3 + 3 + 1.5 = 91.5 inches. Step 2: cut the fabric panel at 91.5 inches. Verify by subtraction: 91.5 − 6 − 1.5 = 84 ✓. Sensitivity: a 4-inch curtain hem raises the cut length to 84 + 8 + 1.5 = 93.5 inches — 2 inches more per panel.
Frequently asked questions
How deep should my hem be for different garment types and fabrics?
Hem depth depends on garment type, fabric weight, and desired drape. Standard guidelines: lightweight blouses and tops: 1/2 to 1 inch; midweight skirts and dresses: 1 to 2 inches; trousers: 1.25 to 1.5 inches (cuffed trousers may have larger turn-ups); coats and jackets: 1.5 to 2.5 inches with weight to help the hem hang; curtains and drapes: 3 to 4 inches at the bottom (the weight pulls the curtain straight); chiffon and sheer fabrics: 1/4 to 1/2 inch rolled hem or 2-inch double-fold hem for a structured look; knits: 3/4 to 1 inch with twin-needle or coverstitch. Curved hems (circle skirts, A-line dresses) need to be narrower (1/2 to 1 inch) because the curved fabric resists turning under flat. Vintage and couture garments sometimes have very deep hems (4–6 inches) which allow future length adjustments and add elegant weight. Always test your hem depth on a fabric scrap first to confirm it presses cleanly without puckering.
What is the difference between a single-fold, double-fold, and blind hem?
A single-fold hem turns the raw edge up once and stitches it down — the simplest option but leaves the raw edge visible inside. It works for fabrics that don't fray (felted wool, fleece, leather) or when the raw edge is finished separately (serged, pinked, or bound). A double-fold hem turns the raw edge under by a small amount (about 1/4–1/2 inch), then folds the hem up its full depth and stitches near the inner fold — the most common and durable garment hem, using hem depth + turn-under of fabric. Curtains often use a full double hem instead, folded up by the hem depth twice (2 × depth). A blind hem stitches the hem with the bulk of the stitching hidden inside the fold, showing only a tiny visible stitch every few inches on the outer face — used in trousers, formal skirts, and tailored garments where you don't want a visible stitch line. Blind hems use a special foot and zigzag-with-skip stitch pattern. Rolled hems and machine-rolled hems (with a rolled hem foot) are a variant of single-fold for very fine fabrics, creating a narrow 1/8-inch finished hem. Choose based on fabric, garment style, and desired finish quality.
How do I hem curved or shaped edges like circle skirts and A-line dresses?
Curved hems require narrower hem depths (1/2 inch maximum, 1/4 inch often better) because the outer curve of the hem must compress to match the inner curve of the garment. Options for curved hems: (1) Narrow rolled hem using a rolled hem foot — best for very lightweight fabrics. (2) Two rows of stitching: stitch 3/8 inch from the edge, fold up using the stitch as a guide, stitch 1/4 inch from the fold, trim excess fabric close to the second stitch line. (3) Bias tape: bind the curved edge with single-fold or double-fold bias tape, eliminating the need to fold the fabric itself. (4) Easing in the curve: machine-baste 1/4 inch from the edge, gather slightly to ease the outer curve, then press the hem turn-up flat — labor-intensive but produces a flat, professional result. (5) Faced hem: cut a curved facing piece that mirrors the hem, stitch right-sides together, turn, and topstitch — adds weight and a clean finish. For circle skirts in particular, hang the skirt for 24–48 hours before hemming so the bias-cut sections drop out before you measure final length.
What are common mistakes when planning hem and seam allowances?
The most common mistake is forgetting the seam allowance at the top of the panel — cutting only finishedLength + hem fabric, then ending up with a garment 5/8 inch too short. Another error is treating the hem depth as the whole hem allowance (cutting just 1 inch extra for a 1-inch hem) when a double-fold hem also needs the turn-under (about 1/2 inch), or a full second fold (2× the depth) for a curtain double hem. Pre-washing matters: unwashed natural fibers (especially 100% cotton or linen) can shrink 3–8% in the first wash, making a planned 24-inch skirt come out at 22.5 inches after one laundry cycle — always pre-wash and dry your fabric the way the finished garment will be cared for. Forgetting that the bottom hem and top seam allowance combine into total cut length leads to running short by 1–3 inches per panel. Using the same hem depth for very curved edges results in puckering — narrow the hem on curves. Failing to allow for pattern matching across panels adds 5–15% to fabric needs but is often overlooked at the cutting stage. Finally, not double-checking the math before cutting: a single number error in cutLength wastes the entire panel.
When should I NOT use this calculator?
Skip this formula for serged/overlocked single-fold hems where only the depth (no turn-under) needs to be added. Do not use it for bias-cut garments where the fabric stretches under its own weight and hem allowances must be calculated after the garment has hung for 24–48 hours to settle. Avoid it for circle skirts, peplums, and other heavily curved hems where standard double-fold construction does not work; use bias binding or rolled hems instead. The formula does not apply to knit garments with raw-edge hems (popular in t-shirts and athletic wear) where no hem is folded. For lined garments where the lining provides the hem finish, use lining-specific calculations. Do not use it for tailored trousers with cuffs/turn-ups; those have specific turn-up depths (typically 1.5 inches visible + extra for the hem above the turn-up). For shaped hem bands or contrast banded hems, the band length and seam allowance replace the formula entirely. Finally, for any couture garment with hand-finished hems, planning needs to account for hand-stitching technique (catch-stitching, hemming stitch, blind-hem stitch) and the extra width those require.
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