Blanket Size, Yarn & Blocking Calculator
Yarn goes as area, so 10% bigger costs 21% more. Backwards, 2.5× the yarn buys only 1.58× the size.
"A bit bigger" costs more than a bit
People scale blankets in one dimension in their heads and buy yarn the same way. But yarn is used per square inch, so scaling both directions by s multiplies the yarn by s squared. Ten per cent bigger is not ten per cent more yarn.
| Bigger by | Size | Yarn | Extra |
|---|---|---|---|
| — | 50×60″ | 1000 yd | — |
| 5% | 53×63″ | 1103 yd | +10% |
| 10% | 55×66″ | 1210 yd | +21% |
| 20% | 60×72″ | 1440 yd | +44% |
| 25% | 63×75″ | 1563 yd | +56% |
| 50% | 75×90″ | 2250 yd | +125% |
| 100% | 100×120″ | 4000 yd | +300% |
Ten per cent bigger each way is 21% more yarn; twenty per cent is 44%. A "slightly larger" blanket routinely runs a skein or two short — and it runs short at the very end, in a dye lot the shop stopped carrying months ago.
Backwards, it is worse — and more useful
The question people actually ask is the other one: I have this much yarn left, how much bigger can I make it? Because area goes as the square, size goes as the square root, and that compresses hard:
two and a half times the yarn buys 1.58× the dimensions
So a whole extra skein on a nearly-finished blanket is a couple of inches, not another foot. That compression is exactly why "I'll just keep going until the yarn runs out" ends in a blanket of the wrong shape — you spend a lot of yarn moving the edge very little, and then you stop mid-row. Decide the size first and buy for it.
Blocking grows the two directions differently
Everyone knows a blanket grows when it is blocked. What gets missed is that it does not grow evenly — lace in particular opens far more along one axis than the other, because the stretching is doing quite different work to the stitches than to the rows. Measure your swatch before and after in both directions and keep the two numbers apart.
On an aggressively blocked lace piece growing 20% across and 35% up, taking one figure for both puts the width out by 4.6 inches. And the arithmetic is a division, not a subtraction: to finish at 50 inches after 10% growth you knit 50 ÷ 1.1 = 45.45, not 50 − 10% = 45. That gap is small at small growth figures and grows with them — at 35% it is over four inches.
This tool takes both directions separately and shows what each shortcut would have cost you on your own numbers.
Notes
- Get the yarn density from a swatch, not a chart. Work a square, measure it, and note how much yarn it took. That figure knows your yarn, your hook and your stitch pattern; no table does. It is also the same swatch you needed for gauge and blocking.
- The presets are conventions, not standards. Blanket sizing varies between makers and countries, which is why the boxes take free measurements and the presets are only a starting point.
- Add a margin for edging. A border is worked on the finished area and can add several inches all round, so decide whether your target size includes it before you buy yarn for it.
- Buy the whole quantity in one dye lot. A blanket is the largest flat expanse you will ever knit, which makes it the place a lot change is most visible.
How to use
- Pick a preset size or type your own finished dimensions.
- Enter the blocking growth for each direction, measured from a swatch.
- Give the swatch size and the yarn it took for a yarn estimate.
- Knit to the pre-blocked size shown, not to the finished size.
Frequently asked questions
How much yarn does a blanket take?
Its area times your yarn-per-square-inch, which you get by measuring a swatch and noting the yarn it used. The important part is that it is an AREA calculation — people scale blankets in one dimension in their heads and then buy yarn as if that were the whole change.
How much more yarn does a bigger blanket need?
The square of the scale. Ten per cent bigger in each direction is 21% more yarn; twenty per cent is 44%; half again is 125%. This is why a "slightly larger" blanket runs a skein or two short — and it runs short at the very end, in a dye lot the shop no longer stocks.
I have leftover yarn. How much bigger can I go?
Much less than you would think, because size goes as the square root of the yarn. Two and a half times the yarn buys only 1.58 times the dimensions, so an extra skein on a nearly-finished blanket is a couple of inches rather than another foot. That compression is why "keep going until it runs out" ends in the wrong shape.
What size should I knit so it blocks to the right size?
Divide by the growth, do not subtract it. To finish at 50 inches after 10% growth you knit 50 ÷ 1.1 = 45.45, not 50 − 10% = 45. The gap is small at small growth figures and grows with them — at 35% growth it is over four inches.
Does blocking grow both directions the same amount?
Often not, and lace especially not — it can open far more along one axis than the other, because the stretching does quite different work to the stitches than to the rows. On a piece growing 20% across and 35% up, using one figure for both puts the width out by 4.6 inches. Measure your swatch in both directions.
How do I measure blocking growth?
Measure the swatch, wet it and block it exactly as you will the blanket, let it dry completely, and measure again — width and height separately. It is the same swatch you needed for gauge and for the yarn density, so one swatch answers three questions.
What are standard blanket sizes?
There are conventions rather than standards, and they vary between makers and countries. The presets here run from a 14-inch lovey through baby, lapghan and throw sizes up to king, but treat them as a starting point and measure the bed or the person if it matters.
Should I allow extra for a border?
Yes, and decide before you buy yarn. A border is worked around the finished area and can add several inches all round, which by the area arithmetic above is a lot more yarn than it sounds. Work out whether your target size includes the edging or not.
Does this send anything anywhere?
No. Everything is calculated in your browser and nothing is stored or uploaded.
🔒 This tool runs entirely in your browser. Nothing you enter is uploaded, logged, or stored.