How this amigurumi calculator works
Resizing an amigurumi is one of the most common — and most commonly botched — tasks in crochet. People reach for the wrong formula because the physics changes depending on what you are changing. This tool splits the problem into two distinct scenarios so you always apply the right math.
Scenario A: same pattern, new hook or yarn (linear scaling)
This is the situation most crocheters actually face. You have a pattern that calls for 100 g of worsted yarn at 20 stitches per 10 cm, and you want to make the same amigurumi using DK yarn at 28 stitches per 10 cm. The stitch count in the pattern does not change — only the size of each individual stitch changes. Because total yarn is the sum of yarn-per-stitch × stitch-count, and yarn-per-stitch is proportional to stitch length, the total yarn scales linearly with the ratio of gauges.
The formula is:
new_yarn = original_yarn × (original_gauge ÷ target_gauge).
The finished size scales by the same ratio. So switching from 20 to 28 stitches
per 10 cm makes the piece about 71% of the original size and uses about 71% of
the yarn.
A critical caveat: do not assume that halving the hook size halves the gauge. Gauge is dominated by the yarn’s physical thickness, not the hook number. A 4 mm hook with DK yarn produces a very different gauge than a 4 mm hook with worsted. That is why this calculator lets you specify gauge either directly (stitches per 10 cm from a real swatch) or by selecting a yarn weight class, which looks up a typical gauge band from the Craft Yarn Council standard.
Scenario B: same yarn, resize the pattern (cubic scaling)
Sometimes you want to keep the exact same yarn and hook but make the finished piece larger or smaller than the designer intended — a 15 cm bunny becomes a 30 cm bunny. To do this you must rewrite the pattern, scaling the stitch count in every round. Because an amigurumi is roughly a 3D solid, every linear dimension (height, width, depth) scales together, so the total volume — and therefore the total yarn — scales with the cube of the linear size factor.
The formula is:
new_yarn = original_yarn × scale³.
Doubling the size (2×) requires 8× the yarn, not 2×. This catches many makers
by surprise and is the single biggest reason hand-dyed yarn runs out mid-project.
The "Resize pattern" mode in the calculator above applies this cubic formula
and warns you when the scale is extreme.
Why gauge, not hook size, drives the calculation
Many online calculators ask you for "original hook" and "new hook" and apply a simple ratio. This is misleading. The hook is just a tool; the gauge is the physical reality. Two crocheters using the same hook and yarn can produce gauges 30% apart because of tension differences. A swatch is the only honest input. If you cannot swatch, picking a yarn weight class and using its typical gauge band is a more honest estimate than assuming hook size alone.
For amigurumi specifically, you want a tighter gauge than for garments so the stuffing does not leak through the stitches. Most amigurumi designers recommend going down one hook size from the yarn label’s recommendation. Keep that in mind when reading the gauge this tool suggests for a given yarn weight.
Practical worked example
A pattern calls for 80 g of worsted yarn at 22 stitches per 10 cm. You want to use DK yarn instead. From the yarn weight table, DK typically gauges around 26 stitches per 10 cm. Using linear mode: scale = 22 ÷ 26 ≈ 0.846. New yarn = 80 × 0.846 ≈ 68 g. Finished size ≈ 85% of the original. If you instead wanted to keep the worsted yarn but upscale the pattern by 1.5×, switch to cubic mode: 80 × 1.5³ = 80 × 3.375 = 270 g. Same starting number, very different answer.
Calculating yarn yardage vs. yarn weight
Many crocheters ask for "yarn yardage" rather than "yarn weight" — and the distinction matters. Yardage is the total length of yarn in metres or yards, while weight is the total mass in grams. Most amigurumi patterns list yarn by weight (e.g. "100 g of worsted"), but when you are substituting yarns or buying from a brand that labels by yardage, you need to convert. The rule of thumb: a standard 50 g skein of worsted yarn contains roughly 85–95 metres (93–104 yards), but this varies by fibre — cotton is denser than acrylic, so the same weight gives you less yardage. This calculator works in grams because gauge ratios are more reliable that way, but if you need yardage, multiply the gram result by your yarn's metres-per-gram ratio (found on the ball band). For example, if the calculator says you need 68 g of DK yarn and your skein lists 120 m per 50 g, that is 2.4 m/g — so 68 × 2.4 = 163 metres (178 yards) of yarn yardage needed.
Limitations and accuracy
No calculator can perfectly predict yarn use because hand tension varies, colour changes waste yarn, and amigurumi shapes are not perfect solids. Treat these results as guidance with roughly ±15% uncertainty. Always buy a little extra yarn from the same dye lot — running out with 5 g to go is the oldest heartbreak in crochet. The PDF this tool exports is designed to be printed and taken to the yarn shop.