Yarn substitution calculator
Enter what the pattern asks for and what is on your ball band. You get the number of skeins to buy, plus an honest read on whether the two yarns are close enough to behave the same way.
How this is calculated
The rule most people get wrong
When you substitute a yarn and match the pattern's gauge, you are making the same fabric: same stitches, same size, same volume. What stays roughly constant is therefore the weight of yarn, not its length. Buying "the same yardage" is the classic mistake, and it goes wrong in whichever direction your substitute differs.
So the calculation is:
- Convert whatever the pattern states into grams, using the original yarn's ball band.
- Divide those grams by your substitute's skein weight.
- Round up — you cannot buy 6.3 skeins.
The compatibility check
Yards per gram is a direct, measurable statement of how fine a yarn is, and it is far more reliable than the name on the label — "DK" from one brand routinely overlaps with "worsted" from another. The tool compares the two and tells you how far apart they are:
| Difference in yards per gram | What it means |
|---|---|
| Under 10% | Genuinely similar. Gauge should match with the same needles. |
| 10–25% | Workable, but expect a needle size change and swatch first. |
| Over 25% | Different fabric. The finished piece will not behave like the pattern. |
What the numbers cannot tell you
Fibre content changes drape, weight and how the piece ages, and no calculation reaches it. Cotton is heavy and has no spring, so ribbing sags. Alpaca grows as it hangs. Superwash wool relaxes in the wash. Match the quantity here, then decide separately whether the fibre suits the garment.
Not working from a pattern at all? The yarn calculator works it out from your own swatch and project size, and how much yarn for a blanket has every standard blanket size ready to tap.
Questions people actually ask
Why not just buy the same number of yards the pattern asks for?
Because yardage describes the yarn, not the fabric. Two yarns can both be called worsted and still differ by 30% in yards per gram. If you match yardage with a denser yarn you end up with a heavy, stiff fabric and leftover skeins; with an airier one you run out. When you are matching gauge, the thing that stays roughly constant is weight, because you are making the same volume of fabric.
What does yards per gram actually tell me?
It is a direct measure of how fine the yarn is: more yards packed into each gram means a thinner strand. It is more honest than the label category, because 'DK' and 'worsted' overlap heavily between brands. If two yarns are within about 10% of each other on yards per gram, they are genuinely similar. Beyond 25% apart, you are changing the fabric, not substituting.
The tool says my substitution is risky. Can I still do it?
Yes, but go in with open eyes. A thinner yarn on the same needles gives a looser, drapier, more see-through fabric and a larger finished piece; a thicker one gives a dense, stiff fabric and a smaller piece. For a scarf or blanket that may be perfectly fine, even desirable. For a fitted garment it will not fit. The warning is about what changes, not about permission.
Does fibre matter, or only thickness?
Both, and fibre is the part no calculator can price in. Cotton is heavier than wool for the same length and has almost no memory, so a cotton substitute in a ribbed sweater will sag. Alpaca grows lengthwise as it hangs. Superwash wool relaxes more when washed. The numbers here get you the right quantity; whether the fibre suits the garment is a judgement you still have to make.
How accurate is this?
The arithmetic is exact — it is your two ball bands and division. The assumption underneath it is that you will match the pattern's gauge, which is the normal reason to substitute. If you are not matching gauge, the finished size changes and so does the amount, and no calculator can tell you by how much. The only certain answer is to swatch in the substitute and use the yarn calculator.
Last checked: 2026-08-09