A fabric grading calculator determines Pattern Adjustment Ratios for stretch fabrics and scales base-size patterns across a size range. Enter your fabric's stretch percentage to get the exact reduction factor, then grade patterns up or down with proportional measurement adjustments per body zone.
Measurements
Grading Results
Quick Fraction Reference
Precision Drafting Gear
When drafting custom patterns for stretch fabrics, guessing your measurements with a cheap cloth tape that stretches over time will ruin your fit. We strongly recommend upgrading to a fiberglass measuring tapethey never warp or stretch out of calibration. For drawing your newly calculated curves, a clear acrylic French curve set is essential. Being able to see your previous markings through the ruler ensures perfectly blended armholes and necklines every time.
How to Calculate Pattern Adjustment Ratios (PAR)
Drafting patterns for stretch fabrics (like spandex, jersey, or swimwear) is entirely different from drafting for woven cottons. Woven fabrics don't stretch, so you add "ease" to the pattern to allow the body to move. Stretch fabrics require negative easethe pattern must be drafted smaller than the body so the fabric stretches to fit like a second skin. To calculate exactly how much smaller to make the pattern, you must find your fabric's Pattern Adjustment Ratio (PAR). PatternScale automates this critical math. You simply measure a 4-inch block of your fabric, stretch it comfortably against a ruler, and input that stretched length. PatternScale instantly calculates the exact decimal ratio (e.g., 0.85) you need to multiply against your body measurements to draft a perfectly fitting stretch garment.
Frequently Asked Questions
What is Pattern Adjustment Ratio for stretch fabric?
Pattern Adjustment Ratio (PAR) is the percentage you reduce a pattern designed for woven fabric when cutting stretch fabric. It is based on the fabric's stretch percentage: PAR = 1 / (1 + stretch%). For a fabric with 25% stretch, PAR = 1/1.25 = 0.80, meaning you cut the pattern at 80% of the original width.
How do you measure fabric stretch percentage?
Fold the fabric to get a double layer, mark 10 inches of relaxed fabric, then stretch it until it resists further without distorting. Measure the stretched length. Stretch % = (Stretched - Original) / Original × 100. If 10 inches stretches to 12.5 inches, that is 25% stretch.
What is pattern grading in fashion design?
Pattern grading is the process of proportionally scaling a base-size pattern up or down to create a range of sizes. Each measurement point (bust, waist, hip, shoulder, sleeve) increases or decreases by a specific grade rule — not a uniform scale. Professional grade rules vary by body area: hips grade more per size than shoulders.