How much can I let out a garment?

You can only let out as much as the existing seam allowance allows. Most ready-to-wear garments have 1-1.5cm seam allowances. You must leave at least 0.5cm seam allowance after letting out for the seam to hold.

How do I check the seam allowance?

Turn the garment inside out and measure from the stitch line to the raw edge. This is the available seam allowance. Check at multiple points as it may vary along the seam.

What if there is not enough seam allowance?

Options include: adding a gusset (fabric insert) at side seams, adding a panel at centre back, using decorative tape over the seam, or adding side panels. These require additional fabric.

Will letting out leave a mark from the original seam?

Often yes, especially on dark fabrics. Press with steam and a cloth. For stubborn marks, try a vinegar solution or commercial fabric eraser. Some fabrics (silk, velvet) may show permanent marks.

SewCalcs

Letting Out Calculator — Seam Allowance Check

Check seam allowances and calculate letting-out possibilities.

Current Measurement

Desired Measurement

Current Seam Allowance

Measure inside the garment

Number of Seams

How We Calculate This

The calculator checks whether your seam allowance is sufficient to let out the garment by the desired amount. A minimum of 0.5cm seam allowance must remain.

The formula

Total increase = Desired - Current measurement

Per side = Total increase ÷ Seams ÷ 2

New seam allowance = Original SA - Per side

Possible if new SA ≥ 0.5cm

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates. Always verify quantities before cutting or purchasing fabric.