How we calculate
Every calculator follows a published standard or common craft practice, shows its formula on the page, and is tested against examples worked out by hand before it goes live.
The Craft Mat is run by one person, Khokhar Sab, a developer who doesn't quilt, knit or crochet. "We" on this site means Khokhar Sab. That's why nothing here relies on personal habit: the method is written down and checked so you can follow it yourself.
Sources
- Yarn weights, gauges, hooks and needles: the Craft Yarn Council's standards at www.YarnStandards.com, presented in our own tables.
- Quilting: common quilt and batting sizes, the usable width of quilting cotton after selvages are trimmed, and standard binding strip widths. These vary by brand, so every preset can be edited.
- Blanket, hat and mattress sizes: common sizes from published size charts. Sources differ by a few inches, so the calculators always accept your own measurements.
A worked check
Here is how one result is verified, using the quilt calculator's default queen quilt (90 × 95 inches, 4 inches of extra backing per side, 42 inch fabric).
- Backing must be 90 + 8 = 98 inches wide and 95 + 8 = 103 inches long.
- 42 inch fabric minus 2 inches of selvage leaves 40 inches usable.
- Seams across the quilt: 103 ÷ 40 = 2.6, so 3 panels, each 98 inches long. 3 × 98 = 294 inches, which is 8.17 yards, rounded up to 8¼.
- Seams down the quilt: 98 ÷ 40 = 2.5, so 3 panels, each 103 inches long. 3 × 103 = 309 inches, which is 8.58 yards, rounded up to 8⅝.
- The calculator recommends 8¼ yards with horizontal seams. That exact case is one of its automated tests.
Automated tests
Each calculator's math lives in a small separate module. Before release it must pass these test cases, each one checked by hand, including awkward inputs such as very small projects, very large ones, metric measurements and invalid entries.
| Tool | Test cases |
|---|---|
| Quilt calculator | 17 |
| Quilt backing calculator | 7 |
| Binding calculator | 7 |
| Fabric yardage calculator | 5 |
| HST and flying geese calculator | 6 |
| Quilt layout calculator | 10 |
| On-point setting calculator | 8 |
| Blanket yarn calculator | 12 |
| Granny square calculator | 16 |
| C2C crochet calculator | 5 |
| Temperature blanket planner and tracker | 13 |
| Crochet hat size calculator | 9 |
| Foundation chain calculator | 12 |
| Amigurumi ball calculator | 9 |
| Row counter | 15 |
| Yarn yardage converter | 8 |
| Gauge calculator | 5 |
| Increase and decrease evenly | 10 |
| Cast-on calculator | 7 |
| Top-down raglan sweater calculator | 6 |
| Sock calculator | 5 |
| Yarn substitution calculator | 5 |
| Needlepoint canvas size | 4 |
| Fabric count converter | 27 |
| Cross stitch floss calculator | 12 |
| Site search | 6 |
| Total | 246 |
Estimates and margins
Yarn use changes with tension, stitch pattern and fiber. When a result depends on those, we label it an estimate and add a safety margin, usually 10 to 15 percent, which you can change. Your own swatch beats a general estimate, so the yarn tools let you enter one.
Review before publishing
The photos of yarn, fabric and tools are illustrations of materials, never finished projects presented as real work. Every formula must pass its hand-checked test cases, and Khokhar Sab reviews each page before it goes live. More on this in our editorial policy.
Corrections
Found a mistake? Get in touch. Corrections are made, the page's review date is updated, and the change is listed here.
- : Quilt calculator: backing panels now allow for the fabric each seam uses (½ inch per side), so borderline sizes get an extra panel instead of coming up about an inch short.
- : Crochet hook chart: US Q corrected from 16 mm to 15.75 mm.
- : Quilt calculator FAQ: clarified that 2 inches is taken off the fabric width for selvages.
- : Increase and decrease calculator: instructions now group longer sections so they are easier to follow.