Turn finished measurements into cutting values by adding practical seam allowances.
Hem allowance is often larger than side seam allowance because it is folded back differently at the garment edge.
Formula: Cutting width = finished width + two side seam allowances. Cutting height = finished height + top seam allowance + hem allowance.
Example: A 40 cm finished panel with 1.5 cm side seams becomes 43 cm wide at cutting stage.
Finished garment measurements are not the same as cutting measurements. The moment you add seam allowance, hem allowance or a fold-back edge, the fabric pieces must be larger than the visible finished result.
This is one of the easiest places to make a costly mistake in sewing. A seam allowance calculator helps turn the intended finished dimensions into cutting values before marking or trimming fabric.
Side seams are usually designed for joining pieces together, while hems are designed for folding and finishing edges. Because those operations serve different purposes, the amount of extra fabric needed is often different too.
Separating these values gives a more realistic cutting size and helps avoid over-cutting small pieces or underestimating the depth needed at the hem.
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