Patterns from different countries default to different measurement systems, and gauge, garment measurements, and yarn weight each convert differently. Getting them mixed up is one of the more common ways a project comes out the wrong size.
Length: centimeters and inches
1 inch = 2.54cm. 1cm = 0.3937in. To convert inches to centimeters, multiply by 2.54. To convert centimeters to inches, divide by 2.54.
| Inches | Centimeters |
|---|---|
| 28in | 71cm |
| 32in | 81cm |
| 36in | 91cm |
| 40in | 102cm |
| 44in | 112cm |
| 48in | 122cm |
Gauge: stitches per 4 inches and per 10cm
Gauge doesn't convert with the same simple ratio as a flat measurement, because it's a density figure. To go from stitches per inch to stitches per 10cm, multiply stitches-per-inch by 3.937 (10 divided by 2.54). The gauge calculator handles this conversion directly from your swatch counts.
Weight: grams and ounces
1oz = 28.35g. 1g = 0.0353oz. A standard 100g skein equals approximately 3.53oz, which is why many US yarn labels list both 100g and "3.5oz" for the same skein.
Length of yarn: yards and meters
1yd = 0.9144m. 1m = 1.0936yd. For quick mental math on a skein label, meters run a little longer than yards, so a skein listing both will show a slightly higher meter number than yard number.
When a pattern mixes systems, convert everything to one system before you start swatching. Working gauge in stitches-per-inch while cross-checking garment measurements in centimeters is where math errors creep in, even for careful knitters and crocheters.