Fit & finishing / FREE CALCULATOR
Seam & hem allowance calculator
Calculate a rectangular panel’s cutting size from its finished length and width. Add side and top seams plus a single or double-fold bottom hem, with every allowance shown separately.
Make your calculation
HOW IT WORKS
Enter the finished rectangular panel dimensions.
Add the seam allowances and the actual depth of each hem turn.
Use the cutting size and review the breakdown before marking fabric.
THE WORKING BEHIND THE NUMBER
A little more clarity.
THE METHOD
Cut width = finished width + 2 × side seam allowance. Cut length = finished length + top allowance + first hem turn + second hem turn, when used.
Use finished measurements consistently
A finished measurement describes the part left after seams and hems have been sewn. The cutting measurement adds the fabric consumed by that construction. This tool keeps the two figures separate so you can avoid adding an allowance twice.
The panel is rectangular, with the same seam allowance on both sides. Top and bottom allowances are entered separately. A garment with shaped sides, curved hems or asymmetric edges needs its own pattern treatment rather than a single rectangular calculation.
Add the depth of every turn
For a double-fold hem, enter the first turn and the second turn as separate depths. A 1 cm first turn followed by a 2 cm second turn consumes 3 cm of fabric in total. These fields describe fabric consumed, not a visual width estimated from the outside.
Thickness, fabric behaviour and finishing method can affect the practical result. Sew a sample of an unfamiliar hem and check your pattern’s instructions. The diagram shows where the allowances sit and is not a full-size cutting template.
A FEW USEFUL ANSWERS
Before you cut.
Does a double-fold hem use twice the second fold?
Not necessarily. Add the actual first and second turn depths. They may be different, such as 1 cm followed by 2 cm.
Can this offset a curved pattern piece?
No. It calculates the outer dimensions of a rectangular panel. Curved edges and intersections need a proper pattern offset and corner treatment.
Is ease included?
No. Enter the finished size you already want, including any chosen design ease. This calculator then adds construction allowances.