Should I always pre-wash fabric?

Yes, pre-washing is strongly recommended for garments that will be washed. It removes sizing, preshrinks the fabric, and tests for colour fastness. The only exceptions are fabrics intended for dry cleaning only (like some wools and silks) or interfacing.

How much does cotton shrink?

Standard quilting cotton shrinks about 3–5% in length and 1–2% in width. Cotton flannel can shrink 5% or more. Pre-washed or pre-shrunk cotton (labelled as such) will shrink much less, typically under 1%.

Does fabric shrink more in length or width?

Most woven fabrics shrink more in the lengthwise (warp) direction than the crosswise (weft) direction. This calculator applies the shrinkage rate to length. For width, expect roughly half the lengthwise shrinkage rate.

How do I test my fabric shrinkage rate?

Cut a 30cm × 30cm square, press it, then wash and dry it exactly as you plan to care for the finished garment. Measure again. The percentage change in each direction is your shrinkage rate. Use the custom option in this calculator to enter your tested rate.

SewCalcs

Fabric Shrinkage Calculator — Pre-Wash Allowance

Calculate how much extra fabric to buy to account for shrinkage when pre-washing.

Finished Length Needed

Length you need AFTER pre-washing

Fabric Type

Select fabric type or custom rate

How We Calculate This

To end up with the correct amount of fabric after pre-washing, you need to buy more than you need. The formula accounts for the shrinkage so your post-wash fabric matches your requirements.

The formula

Pre-wash length = Finished length ÷ (1 − Shrinkage%/100)

For example, if you need 2m of fabric and it shrinks 5%: 2 ÷ 0.95 = 2.11m. Buy 2.2m to be safe.

Frequently Asked Questions

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Interfacing Calculator

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Lining Fabric Calculator

Calculate lining fabric requirements for garments and bags.

Last updated: February 2026

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