Convert inches to centimeters.
1 inch = 2.54 cm exactly.
Inches are used for measurements in the United States, and many patterns, tools, and notions are sold in inches. One inch is exactly 2.54 centimeters, so you multiply the inches by 2.54 to get centimeters. A quarter inch is 0.635 centimeter and five eighths of an inch is about 1.59 centimeters.
This is useful when you work from a pattern that is written in inches but you own metric tools, or when you share a pattern with someone who measures in centimeters. Rotary cutters and rulers often show both units.
When you convert a whole pattern, use the same method for every measurement, so the pieces stay in proportion. Rounding each piece differently can make the pieces fail to fit together, particularly where several seams meet.
For sewing, round to the nearest millimeter, and for a quilt, mark the cutting lines carefully since small errors add up across many pieces. It helps to convert the seam allowance first and use a matching foot or guide on your machine.
Handy conversions: 1 inch is 2.54 centimeters, 2 inches is 5.08, 6 inches is 15.24, 12 inches is 30.48, and 36 inches, one yard, is 91.44 centimeters. A quick mental estimate is to multiply by two and a half. Keep a conversion chart near your cutting table if you often switch between the two systems, and always double check a measurement that is critical to the fit of a project before you cut your fabric.