Are calculator results exact?
They are planning estimates based on the measurements you enter. Fiber, stitch pattern, tension, blocking and finishing can change the real result, so a project swatch remains the best evidence.
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Fiber arts formula library
The math behind FiberTools, written so you can audit it, calculate by hand, or understand why a result changes.
Last reviewed: August 7, 2026
Formula index
Gauge from a swatch
stitches per inch = stitches counted ÷ measured width
rows per inch = rows counted ÷ measured height
Worked example: If 22 stitches span 4 inches, the gauge is 22 ÷ 4 = 5.5 stitches per inch.
Open the gauge calculator →Stitches for a target width
raw stitch count = target width × stitches per inch
working stitch count = raw count rounded to a whole stitch or pattern multiple
Worked example: At 5.5 stitches per inch, a 36-inch width starts at 36 × 5.5 = 198 stitches before construction adjustments.
Open the cast-on calculator →Resize a stitch count for your gauge
new stitch count = original stitches × your gauge ÷ pattern gauge
Confirm the finished size and round for the construction repeat.
Worked example: A 120-stitch section written at 20 stitches per 4 inches becomes 120 × 22 ÷ 20 = 132 stitches at your 22-stitch gauge.
Resize for a new gauge →Swatch-based blanket yarn estimate
project grams = swatch grams × project area ÷ swatch area
planning grams = project grams × 1.10; yards = planning grams × label yards ÷ label grams
Worked example: A 4 × 4-inch swatch weighing 8 g scaled to a 40 × 50-inch blanket estimates 1,000 g, then 1,100 g with the transparent 10% planning buffer.
Estimate blanket yarn →Whole skeins to buy
skeins by length = ceiling(total yards ÷ yards per skein)
For swatch-based estimates, FiberTools also checks weight and uses the larger whole-skein result.
Worked example: 1,050 yards with 220 yards per skein gives ceiling(1,050 ÷ 220) = 5 skeins.
Calculate whole skeins →Circle circumference and diameter
circumference = π × diameter
diameter = circumference ÷ π
Worked example: A 22-inch circumference corresponds to a geometric diameter of about 22 ÷ π = 7.0 inches before ease or fabric behavior.
Plan a crochet circle →Sock target circumference
target circumference = measured foot circumference × (1 − negative ease)
stitch count = target circumference × stitches per inch, rounded for construction
Worked example: A 9-inch foot with 10% negative ease targets 8.1 inches. At 8 stitches per inch, that is 64.8 stitches before repeat rounding.
Calculate sock stitches →Standards and measurement sources
FiberTools uses the Craft Yarn Council category system as a reference for yarn weights, common gauge ranges and hook or needle ranges. The council describes those ranges as guidelines and tells makers to follow pattern gauge.
Frequently asked questions
Are calculator results exact?
Why does FiberTools use a measured swatch for blanket yarn?
Gauge alone measures dimensions, not yarn consumption. Weighing a swatch captures the combined effect of yarn, fiber, stitch pattern, hook or needle, and personal tension.
Why are stitches rounded?
A fraction of a stitch cannot be worked. Tools round to a whole stitch and, where requested, to a pattern repeat or construction multiple.