Fabric shrinkage and prewash purchase calculator

Allowance must reverse the measured ratio

A ten-percent loss leaves ninety percent of the starting length.

Recovering a desired finished length therefore requires division by 0.9. Adding ten percent to the target does not undo a ten-percent loss, because the two percentages use different starting quantities.

The Circle skirt waist radius and cutting size calculator establishes geometric cut dimensions before a wash allowance. Avoid applying the same shrinkage factor again if your pattern dimensions already compensate for it.

Measure along both fabric directions

Lengthwise and crosswise changes can differ.

This page retains separate ratios, and a negative shrinkage result means the sample grew. The required target dimensions must already include your pattern and seam allowances. The sample predicts the stated wash treatment only; later laundering, stretching or different grain orientation can change the outcome.

Use retained dimensions to verify the purchase

Multiply the required prewash length by the measured retained-length ratio. Before purchase-step rounding, this should reproduce the target postwash length. After rounding upward, it should meet or exceed the target. This inverse check makes it easier to detect an accidentally reversed before-and-after entry.

A sample can grow after treatment, producing a retained ratio above one and a negative shrinkage percentage. The calculator preserves that result rather than clipping it to zero. Recheck the sample when growth is unexpected; stretching while measuring and measuring on the bias can change the observations.

Work through the entered example

A sample length changing from 20 to 18 cm retains 90 percent. To finish with 180 cm you need 200 cm before washing, not 198 cm.

Start with this case, then change one input and calculate again. Keep the other assumptions fixed so the result has an interpretable cause. The result table exposes intermediate quantities and units rather than hiding them behind a single headline number.

Use the output in a real plan

Lengthwise and crosswise changes can differ. This page retains separate ratios, and a negative shrinkage result means the sample grew. The required target dimensions must already include your pattern and seam allowances. The sample predicts the stated wash treatment only; later laundering, stretching or different grain orientation can change the outcome.

Before purchasing material or comparing alternatives, check the measurements at the point where they enter the calculation. A mathematically precise answer can still be a poor plan when the measured size, loss allowance or price basis is wrong. Save the input assumptions with any result you intend to reuse.