Pattern Scaling Calculator
Calculates scaled pattern dimensions when you need to resize a sewing pattern up or down by a percentage. Use it when printing patterns at a non-standard scale or grading between sizes.
About this calculator
Scaling a sewing pattern means multiplying every dimension by the same factor so the proportions remain consistent. The scale percentage is first converted to a decimal by dividing by 100, and then multiplied by the original measurement. The formula is: newDimension = originalSize × (scalePercentage ÷ 100). A scale of 100% returns the original size, values above 100% enlarge the pattern, and values below 100% reduce it. For example, scaling a 10-inch seam line to 150% gives 10 × (150 ÷ 100) = 15 inches. Keep in mind that seam allowances are linear and scale with the pattern—so after scaling, you may need to re-true seam allowances back to your standard value if precision fit is critical.
How to use
Your printed pattern piece has an original dart length of 8 inches, but you need to scale the pattern to 115% to fit a larger size. Use the formula: newDimension = 8 × (115 ÷ 100) = 8 × 1.15 = 9.2 inches. Your scaled dart should measure 9.2 inches. Repeat this calculation for every marked dimension on the pattern piece—side seams, notch placements, and grain line lengths—to ensure the whole piece scales uniformly. If your printer allows percentage scaling, set it to 115% and the software will handle all dimensions at once.
Frequently asked questions
How do I scale a sewing pattern to a different size using percentages?
Identify the key measurement that differs between your target size and the pattern size—often the bust or hip circumference—and calculate the ratio: (your measurement ÷ pattern measurement) × 100. Use that percentage in the calculator to find each new dimension. For example, if the pattern's hip is 40 inches and yours is 44 inches, the scale factor is (44 ÷ 40) × 100 = 110%. Apply 110% to every dimension for a proportional grade. Note that height and width may need different scale factors if your proportions differ significantly from the pattern's fit model.
What scale percentage should I use when printing a PDF sewing pattern?
Most PDF patterns include a test square—usually 1 inch or 2 inches—that you print and measure to confirm your printer is reproducing the file at 100%. If your printed square measures correctly, print at 100%. If it measures smaller or larger, adjust the print scale percentage until the test square is accurate. Some patterns are designed for A4 paper but intended for Letter paper (or vice versa), which introduces a small size difference; the test square helps you catch and correct this. Never skip the test square check—even a 2–3% error accumulates across a large pattern piece.
Does scaling a sewing pattern affect seam allowances and notch positions?
Yes—scaling changes every linear measurement including seam allowances, notch distances, and dart placements. If you scale a pattern with a 0.625-inch seam allowance to 120%, the seam allowance becomes 0.625 × 1.2 = 0.75 inches, which may not match your sewing machine's standard foot guides. Many sewists prefer to scale only the internal pattern lines (the finished size lines) and re-draw the seam allowances at the standard value afterward. Similarly, button spacing and buttonhole sizes should be re-evaluated after scaling to ensure they match your actual buttons.