Fabric Shrinkage Calculator

Why Fabric Shrinks

Fabric shrinks because fibers relax and contract when they absorb water and then dry. During manufacturing, yarns are stretched tight on looms or knitting machines, leaving the finished cloth under tension. When you wash the fabric for the first time, water causes the fibers to swell, the tension releases, and the yarns settle into a shorter, denser configuration. Heat from the dryer accelerates the process by driving off moisture quickly and shocking the fibers into place. Natural fibers like cotton, linen, wool, and rayon shrink the most because they absorb water readily. Synthetic fibers like polyester and nylon are hydrophobic and thermally stable, so they shrink very little. Blends fall between the two extremes in proportion to their fiber content.

How to Run a Shrinkage Test

Cut a square test swatch of at least 10 by 10 inches from the fabric you plan to use. Mark a precise measurement reference on the swatch, such as a 20 by 20 centimeter box drawn with a fabric marker, so you can measure the same area before and after washing. Record the before measurements in both directions: length (parallel to the selvage, the lengthwise grain) and width (crosswise grain). Wash and dry the swatch exactly the way you plan to care for the finished project, because hot water and tumble drying cause more shrinkage than cold wash and line drying. Let the swatch return to room temperature, press it lightly, and measure again. Enter the before and after measurements into this calculator to see the shrinkage percentage in each direction.

Calculating Cut Size From Target Finished Size

Once you know your fabric's shrinkage rate, you can work backward from a target finished size to the cut size you need. The formula is cut size equals finished size divided by one minus the shrinkage as a decimal. For example, a 36 inch finished length with 10 percent shrinkage requires 36 divided by 0.9, which is 40 inches of fabric. Length and width usually shrink by different amounts, so calculate each direction separately. This calculator does the math automatically when you enter target finished dimensions in the optional fields. Add a small safety margin of 1 to 2 percent on top of the calculated cut size for cutting error and fabric variation.

Fabric Types and Typical Shrinkage Rates

Typical first-wash shrinkage varies widely by fiber and construction. Untreated cotton woven fabrics usually shrink 3 to 8 percent. Pre-shrunk or sanforized cottons shrink only 1 to 3 percent. Linen is notorious for shrinkage of 10 to 15 percent unless pre-washed aggressively. Flannel shrinks about 5 to 10 percent. Wool can shrink 5 to 15 percent or felt heavily if agitated in hot water. Rayon and viscose shrink 3 to 10 percent. Polyester, nylon, and acrylic synthetics shrink 1 percent or less. Knit fabrics of any fiber generally shrink more than woven fabrics of the same material because the loops have more freedom to relax.