Seams & Construction Calculators
Seam allowances, darts, pleats, gathers, hems and construction detail calculations.
Seam Allowance Calculator
Calculate seam allowance amounts and adjust pattern pieces accordingly.
Dart Calculator
Calculate dart dimensions for shaping bodices, skirts and trousers.
Pleat Calculator
Work out fabric needed for box pleats, knife pleats and inverted pleats.
Gather Calculator
Calculate fabric width needed for gathered sections based on fullness ratio.
Ruffle Calculator
Work out fabric requirements for ruffles and flounces.
Tuck Calculator
Calculate fabric needed for pin tucks, released tucks and decorative tucks.
Piping Calculator
Calculate bias strip and cord needed for piping and welting.
Welt Pocket Calculator
Calculate dimensions for single and double welt pockets.
Zipper Length Calculator
Determine the correct zipper length for garments and projects.
Hem Calculator
Calculate hem allowances and fabric needed for different hem types.
10 free calculators in Seams & Construction
Garment Construction Techniques
Good garment construction starts with accurate seam allowances. In the UK, most commercial patterns include a 1.5cm seam allowance, though some independent pattern companies use 1cm. Understanding what seam allowance is included and adding or trimming accordingly is essential for a proper fit.
Darts shape flat fabric to fit body curves. Bust darts, waist darts and shoulder darts each have specific proportions based on the amount of shaping needed. Pleats and gathers add fullness — box pleats typically use 3× the finished width, knife pleats 2×, and gathers range from 1.5× to 3× depending on fabric weight and desired fullness.
Professional finishing details like piping, welting and binding require precise fabric strip calculations. Piping is cut on the bias for curves, while binding can be cut on the straight grain for straight edges. Zipper length depends on the garment opening — dress zips are typically 55–60cm, skirt zips 18–23cm, and trouser zips 15–20cm.