How to use the fabric shrinkage calculator
- Cut a swatch from your fabric and measure its length and width before washing. Wash and dry it the way you will care for the finished item, then measure it again.
- Enter the four swatch measurements in one unit, such as inches or centimeters.
- Enter the length you need after washing and choose yards, meters or inches.
- Read the shrinkage along the length and across the width, the length to buy and the length to ask for, rounded up to an eighth of a yard, a tenth of a meter or a whole inch.
Formula
shrinkage percent = (before - after) / before x 100
length to buy = length needed / (1 - shrinkage along the length)
width after washing = width on the bolt x (1 - shrinkage across the width)
Check: the length to buy times (1 - shrinkage) equals the length you need. The rounded-up value is what you would ask a shop to cut.
A 10 inch swatch that shrinks to 9.5 by 9.8
A swatch that measures 10 inches by 10 inches before washing and 9.5 inches by 9.8 inches after has shrunk 5 percent along the length and 2 percent across the width. To end up with 3 yards after washing, you need 3 / 0.95 = 3.158 yards, which you would ask for as 3 1/4 yards (3.25). That is 0.158 yards, or 5.3 percent, more than you need.
The width matters too. A fabric 45 inches wide on the bolt will be 45 x 0.98 = 44.1 inches wide after washing. If your pattern needs 44 inches of width, this fabric just fits, and if it needs more you must buy a wider fabric or change the layout.
Wash first or buy extra
You can wash the fabric before cutting, so that it shrinks before the item is made, or you can buy extra to allow for shrinkage later. Washing first is the safer plan for a close-fitting item, because the finished piece will not shrink further. This tool helps with either: it tells you how much is lost, and how much to buy if you pre-wash.
Swatches and different fabrics
Shrinkage depends on the fiber, the weave, the finish and the way you wash and dry. Cotton and linen usually shrink more than synthetic fabrics, and a hot dryer shrinks more than line drying. Test a swatch from the same bolt, since two bolts of the same fabric can differ. For the pattern yardage itself, see the Fabric Yardage Calculator, and for clay, which shrinks as it dries and fires, the Clay Shrinkage Calculator.
More tools for the workshop and home
For related projects around the house and workshop, try the Cabinet Door Size Calculator, Pond Liner Size Calculator and Firewood Cord Calculator.
Assumptions and limits
- The swatch is cut from the same fabric and washed the way you will wash the finished item.
- Shrinkage is the same across the whole piece, along each direction.
- The fabric does not grow or stretch in the wash. The tool refuses sizes larger than before.
- All four swatch measures use the same unit.
- The swatch, the length needed and the width in the form are examples to replace with your own.
Frequently asked questions
Should I wash the fabric before I cut it?
For clothing and anything that will be washed often, many sewers wash first so that the finished piece does not shrink. It is your choice, and this tool works out the extra to buy if you do not wash first or if you wash and want to know the loss.
Why is shrinkage different along the length and the width?
Woven cloth is made of threads in two directions that are held differently when the fabric is made, so they relax by different amounts in the wash. Knits can behave differently again.
Is it enough to add the same percentage?
Not exactly. If a fabric shrinks 5 percent, you need 5.26 percent more, not 5 percent, because the shrinkage applies to the longer length you buy. The tool divides by (1 - shrinkage) for that reason.
How big should the swatch be?
A bigger swatch gives a more accurate measure. Ten inches or 25 centimeters is a common choice, since the percentage is then easy to read, but any size works if you measure carefully.