Fabric Shrinkage Calculator - Cut Size That Shrinks Down to Your Target Size

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Why Fabric Shrinks, and Why It Matters

Almost every natural fabric shrinks the first time it is washed. Cotton can shrink three to five percent, linen even more, and wool can shrink dramatically if it is washed hot. If you cut your pieces to the finished size and then wash the fabric, the finished garment comes out too small. The fix is simple: cut bigger, wash first, or buy with shrinkage in mind. This calculator tells you exactly how much bigger to cut.

Shrinkage is not a defect. It is what fibres do when water and heat relax them. Manufacturers sometimes pre-shrink fabric, but many do not, and even pre-shrunk fabric can shrink a little more. The only safe approach is to assume shrinkage will happen and plan for it, especially for fitted clothes, curtains that must reach the floor, and quilts with exact block sizes.

How This Calculator Works

The maths is straightforward. If a fabric shrinks by five percent, then every 100 cm you cut becomes 95 cm after washing. To end up with 100 cm, you must cut 100 divided by 0.95, which is about 105.3 cm. The calculator does this division for both length and width, because fabric often shrinks differently in each direction. The lengthwise grain and the crosswise grain are made differently, so always check both.

The shrinkage percentage is the key input, and it is worth measuring yourself. Cut a square of fabric, mark its size, wash and dry it exactly as you will wash the finished item, then measure again. The difference, divided by the starting size and multiplied by 100, is your shrinkage percentage. A ten-minute test beats a ruined garment.

How to Use It

Enter the finished size you want after washing, in centimetres or inches. Enter the shrinkage percentage for your fabric. If you do not know it, use five percent for cotton, three percent for polyester blends, and eight percent for linen as rough starting points, then confirm with a test square. Press Calculate and you get the cut size, plus the extra amount to add.

Cut to the larger size, then pre-wash the fabric before you sew, if your pattern allows it. Pre-washing is the most reliable method of all: once the fabric has shrunk, it stays at its new size, and your finished measurements hold. If you cannot pre-wash, for example with a delicate fabric, cut to the calculator size and wash gently.

Worked Example

Imagine a cushion cover that must finish at 100 cm by 80 cm, made from cotton that shrinks five percent. Divide 100 by 0.95 to get 105.3 cm, and 80 by 0.95 to get 84.2 cm. Cut 105.3 by 84.2 cm, wash, and the piece lands close to 100 by 80 cm. The extra is only about five centimetres on the length, but that five centimetres is the difference between a cover that fits and one that does not.

For a fabric that shrinks ten percent, the effect is larger. A 200 cm curtain panel becomes 200 divided by 0.90, which is 222.2 cm. Forgetting that step leaves a curtain 20 cm short, which no hem can fix.

Tips for Shrinkage Control

Wash and dry your test square the same way you will treat the finished item. A hot dryer shrinks far more than line drying, so a test that is line-dried will understate shrinkage for a garment that will be tumble-dried. Keep the test square after washing, with its measurements written on it, as a record for future projects in the same fabric.

Buy a little extra fabric beyond the calculator result. Shrinkage varies across a bolt, and a second wash can take another small amount. An extra ten centimetres is cheap insurance on a large project.

Common Mistakes

The biggest mistake is adding the percentage instead of dividing by it. Adding five percent to 100 cm gives 105 cm, which shrinks to 99.75 cm, close but still short. The correct method, dividing by 0.95, gives 105.26 cm, which lands exactly on target. For small projects the difference is tiny, but for curtains and bedding it matters.

Another mistake is testing shrinkage on a tiny scrap. A five-centimetre scrap is hard to measure accurately, and a one-millimetre error becomes a two percent error. Test with at least a 20 cm square, and measure with a ruler, not by eye.

Frequently Asked Questions

Does shrinkage stop after the first wash? Mostly, yes. The first wash causes most shrinkage. Later washes cause much smaller changes, which is why pre-washing works so well.

Do synthetic fabrics shrink? Much less than natural fibres, but heat can still affect them. Always check the care label, and avoid high dryer heat for synthetics.

Can I un-shrink fabric? Sometimes soaking in lukewarm water and gently stretching helps a little, but it rarely restores the full size. Prevention is far better than repair.

Please note: sewing results here are estimates and guidance only. Fabric, pattern and personal ease vary, so measure twice and buy a little extra.

Fabric Shrinkage Calculator – Cut Size That Shrinks Down to Your Target Size