Inches, yards, centimeters, and meters
Switching units should describe the same piece of cloth. These calculators convert into inches, do the geometry there, and convert the purchase quantity only at the end.
Exact factors
One inch is exactly 2.54 centimeters. One yard is exactly 0.9144 meters, and one yard is 36 inches. One meter is 100 centimeters, which is 39.370078… inches.
Those factors are constants. They are not rounded inside a calculation.
What is allowed to round
A finished size such as 100 stitches ÷ 14 count stays at 7.142857… inches. The page may display 7.14 in, but the stored result is the full value.
Purchase quantities round up to an increment you can edit. The suggested starts are 1/8 yard and 0.1 meter. Nearest-value rounding is not used, because a shop cannot sell the missing fraction.