Garment or seam line
The solid outline is the shape that should sew together: side seams, shoulder seams, armholes, crotch seams, waistlines, and other construction edges.
Sewing pattern guide
Seam and hem allowances
Generated patterns show both the construction line and the cutting line. Understanding the difference helps you print, cut, and test the draft correctly.
Seam allowance is the strip of fabric between the stitch line and the cut edge — the working margin that lets two pieces be joined, pressed, finished, and later let out if a fitting demands it. On every generated pattern it is drawn explicitly: the solid line is where you sew, the dashed line outside it is where you cut. Because the generator adds the allowance for you at the width you choose, your two jobs are choosing sensible widths and never confusing the two lines.
There is no single correct allowance. A straight side seam in a woven skirt, a tightly curved neckline, a zipper opening, and a t-shirt hem each want a different width — wide enough to hold and finish, narrow enough not to fight the curve. Commercial patterns often print one blanket width everywhere and leave the compromises to you; a generated pattern lets you set seam and hem allowances separately, so it is worth knowing what the sensible values are.
This guide covers how allowances work on generated patterns, which widths suit which seam types, and the handling techniques — pressing, grading, clipping, hemming — that turn an allowance from spare fabric into a clean inside finish. The reference table gives concrete numbers you can enter directly into the generator settings.
Visual guide
Solid line, dashed line, and hem allowance
Use the solid line as the sewing or finished edge. Use the dashed line as the cutting line after allowance is added. Lower edges can use a larger hem allowance than regular seams.
Allowance diagram
Cutting line with allowance
The dashed outline sits outside the solid line and shows where to cut after adding seam or hem allowance.
Construction seam allowance
Most regular seams use a smaller allowance, commonly around 1 cm, unless the pattern settings specify another value.
Hem allowance
Lower edges often need more allowance than seams. Pants and shorts may use a 2.5-3 cm hem so the edge can be folded and finished cleanly.
Allowance around curves
On armholes, necklines, crotch curves, and other curved edges, the dashed line must preserve a consistent offset from the original curve.
Corners and transitions
Where two seams meet, allowances must transition clearly so the cutting line does not hide under the garment line or create an accidental wedge.
Generated allowance is still a setting to verify
Allowance values are calculated from the options you choose, but sewing method, fabric thickness, finishing technique, and personal workflow can require changes before production.
Working with allowances
How to choose and handle seam allowances
Decide the widths before generating, because the dashed cutting line is drawn from them. Then let the handling follow the seam: every allowance gets pressed, most get finished, and curved ones get trimmed or clipped so the seam can lie flat.
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01
Read the two lines correctly
The solid outline is the stitch line — the exact geometry the generator drafted and checked, including matched seam lengths. The dashed outline is the cutting line, offset outward by your chosen allowance and drawn parallel even around curves and corners. Cut on the dashed line, sew on the solid one; the distance between them is the allowance you selected, so your machine's seam guide can reproduce it precisely.
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02
Set the width by seam type, not by habit
Straight structural seams — side seams, shoulder seams, centre backs — work well at 1.5 cm: enough to finish and to let out roughly a size later. Tight curves — necklines, armholes that get a facing, crotch curves — want 0.6–1 cm, because a wide allowance on a concave curve bunches and distorts the seam. Zipper openings need 1.5–2 cm so the tape has fabric to sit on.
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03
Enter body measurements and allowances separately
The generator applies allowance after drafting, outside the finished geometry. Never add 'a bit extra for seams' to the measurements themselves — that inflates the garment body by 2–4 cm per circumference and then the allowance is added again on top. Measurements describe your body; the allowance setting describes your sewing margin. Keep the two strictly apart.
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04
Press every seam before crossing it
Sew, then press the seam flat as sewn to set the stitches, then press the allowances open or to one side according to the seam. Do this before another seam crosses it — a waist seam sewn over unpressed side seams locks the lumps in permanently. Pressing means lowering the iron and lifting it, not sliding; sliding stretches bias edges out of shape.
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05
Finish the raw edges to match the fabric
Woven fabrics fray, so finish allowance edges: overlock/serge, zigzag, pinking for stable fabrics, or French seams for sheers (which need about 1.5 cm of allowance to sew in two passes). Knits do not fray — a t-shirt sewn entirely on an overlocker at 0.7–1 cm needs no separate finishing, which is why knit allowances can be narrow.
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06
Grade and clip curved and enclosed seams
Where a seam is enclosed — under a facing, collar, cuff, or pocket flap — trim the allowance layers to different widths (grade them) so the edge steps down gradually instead of leaving a ridge. On concave curves like necklines, clip into the allowance every 1–2 cm up to 2 mm from the stitch line; on convex curves like flap corners and patch pocket bottoms, cut small notches out so the fabric can fold without bunching.
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07
Give hems the depth the garment needs
Hems are the exception to 'narrower is safer': they need depth for weight and a clean fold. A t-shirt hem is typically 2–2.5 cm twin-needled or coverstitched; skirt and dress hems run 2–4 cm (less on flared shapes, where a wide hem cannot follow the curve); pants take 3–4 cm to allow later lengthening. Set the hem allowance separately from the seam allowance in the generator — one value does not serve both.
Recommended allowance widths
Enter these values in the generator settings as a starting point. They assume a mid-weight woven unless stated otherwise; move toward the wider end for thick or loosely woven fabric and for garments you may need to let out, toward the narrower end for fine fabrics and tight curves.
| Seam or edge | Recommended allowance | Why this width |
|---|---|---|
| Side and shoulder seams (woven) | 1.5 cm | Room to finish the edge and let out ~1 size at a fitting |
| Curved necklines and armholes | 0.6–1 cm | Narrow allowance follows the curve; less clipping needed |
| Zipper openings | 1.5–2 cm | Fabric under the zipper tape; easier basting and pressing |
| Waist seams and yokes | 1 cm | Reduces bulk where several layers and darts meet |
| Knit seams (overlocked) | 0.7–1 cm | Matches overlocker stitch width; knits do not fray |
| T-shirt hem | 2–2.5 cm | Depth for a twin-needle or coverstitch finish |
| Skirt and dress hem | 2–4 cm | Weight for a clean drape; narrower on flared shapes |
| Pants and shorts hem | 3–4 cm | Crisp press-fold plus reserve for lengthening |
For a blind hem, plan the deeper end of the hem range and press the fold accurately — the stitch catches only a thread of the outer layer, so the fold itself does the visual work. If you are undecided on a fitted garment, choose 1.5 cm everywhere structural: you can always trim an allowance down, but you cannot add fabric back.
Common allowance mistakes
Adding allowance twice
Padding your measurements 'to be safe' and then also setting a seam allowance in the generator double-counts the margin: the garment comes out 2–4 cm larger per circumference than the preview promised. Enter true body measurements; the dashed line already contains the entire safety margin.
One width everywhere
Setting 1.5 cm on every edge feels tidy but fights you at the neckline (bunching on the curve) and shortchanges the hem (no depth for a fold). Use the separate seam and hem settings — that is exactly why they exist.
Skipping the clips on curves
A neckline or armhole facing sewn and turned without clipping cannot open out — the allowance is shorter than the seam it must now cover, so the edge rolls and refuses to lie flat. Clip concave curves every 1–2 cm, notch convex ones, and stop 2 mm short of the stitch line.
Hemming a bias or flared skirt straight away
Bias-cut and strongly flared skirts drop unevenly under their own weight — often 1–3 cm more at the bias than at the grain. Let the garment hang for 24–48 hours, re-mark the hem level on the body, trim even, and only then press and sew the hem.
Not grading enclosed seams
Leaving all layers full width inside a collar, cuff, waistband, or pocket flap produces a hard ridge that shows through pressing on the right side. Trim the layers to staggered widths — for example 3 mm and 6 mm — so the edge tapers.
Cutting corners diagonally through the stitch line
When trimming bulk at a corner, cut close across the point but never through the stitching, and leave at least 2–3 mm beyond the stitch line. Cutting too close frays open the corner the first time it is turned and poked out.
Allowances as your fitting reserve
Plan wider seams where you expect to adjust
For a first fitted garment from a new block — pants, pencil skirt, fitted bodice — set side seams to 2 cm instead of 1.5. Each extra 0.5 cm per seam edge is 2 cm of circumference across two side seams, enough to rescue a slightly optimistic waist measurement without recutting.
Let out in the right order
If a fitting is tight, open the side seams first — they are straight, easy to resew, and least visible. Press the old crease out fully before restitching, and re-finish the now-narrower allowance. Letting out curved seams (armholes, crotch) changes the drafted geometry; prefer regenerating the pattern with a corrected measurement instead.
Baste before committing on fitted garments
Machine-baste the structural seams at the exact allowance width, try the garment on, and only then sew permanently and trim or finish. Once an allowance is overlocked and trimmed to 0.7 cm, the fitting reserve is gone — finishing is the point of no return.
Fix recurring adjustments at the source
If you let out the same seam by the same amount on every project, the correction belongs in the inputs, not the seams: adjust the measurement or the ease setting and regenerate. The allowance is a per-garment reserve, not a substitute for an accurate draft.
Frequently asked questions
Does the generator add seam allowances automatically?
Yes. You choose the widths in the settings, and the generator draws the dashed cutting line at exactly that offset outside the solid stitch line — kept parallel around curves and resolved cleanly at corners. Enter plain body measurements and let the dashed line carry the entire allowance.
Which line do I cut on — solid or dashed?
Cut on the dashed line; sew on the solid one. Cutting on the solid line removes the allowance completely and shrinks the garment by one allowance width per seam edge — about 3 cm of circumference per seam pair at 1.5 cm settings — and there is no way to add the fabric back.
Can I use different allowances on different edges of one piece?
The generator applies your seam allowance to construction seams and your hem allowance to hem edges, which covers the case that matters most. If a single seam needs a special width — say 2 cm just for a lapped zipper — either set the project-wide value to match or add the extra by hand when cutting that one edge, and mark it on the fabric so you sew at the right distance.
What allowance should I use for knits and an overlocker?
0.7–1 cm, matching the overlocker's stitch width so the knife trims almost nothing. Knits do not fray, so no separate finishing pass is needed. Keep the t-shirt hem at 2–2.5 cm though — a twin needle or coverstitch needs that depth to catch the fold reliably.
How wide should a hem be on a flared skirt?
Narrower than on a straight one: 1–2 cm, or a rolled/faced finish on strong flares. The hem fold-up is a smaller circle than the edge it folds onto, so a deep hem on a flared curve always has excess to ease in. And on flared or bias skirts, let the garment hang for a day or two and re-level the hem before sewing it.