The honest answer is "between 1,500 and 8,000 yards", which is useless. The useful answer comes from two numbers you can establish in an afternoon: the finished size you want, and the gauge you actually get.
Why blanket estimates vary so wildly
Four things move the yardage, and they multiply rather than add:
Size. Area, not length. Going from a 30 by 40 inch baby blanket to a 90 by 90 inch queen is not three times the yarn, it is nearly seven times.
Yarn weight. A thicker yarn covers ground with fewer stitches, but each stitch eats more length. The total weight of yarn for the same blanket is fairly similar across weights, but the yardage is not, because a gram of bulky yarn holds far fewer yards than a gram of DK.
Your gauge. A looser fabric covers more area per stitch and so needs less yarn per square inch. This is the factor people forget, and it is worth about a third either way.
The stitch. Cables, bobbles and dense textured stitches use 20 to 30 percent more yarn than plain stockinette or single crochet over the same area. Lace uses less.
Step one: decide the real finished size
Standard blanket sizes, in inches:
| Name | Size |
|---|---|
| Lovey | 12 x 12 |
| Baby | 30 x 40 |
| Crib | 36 x 52 |
| Throw | 50 x 60 |
| Twin | 65 x 90 |
| Full or double | 80 x 90 |
| Queen | 90 x 90 |
| King | 108 x 90 |
A blanket that has to actually cover a bed needs the full size, not the mattress size. A throw that lives on the sofa can be any size you like, and 50 by 60 inches is a good default because it covers a lap and most of a person.
Step two: measure your gauge
Work a swatch in the yarn and stitch you plan to use, at least 6 inches square, then block it. Measure the stitches over 4 inches across the middle of the swatch.
Write that number down. A typical worsted blanket comes out around 4.5 stitches per inch and 6 rows per inch. A DK blanket is closer to 5.5 and 7.
Step three: work out the total stitches
Multiply the two gauges together to get stitches per square inch, then multiply by the area.
For a 50 by 60 inch worsted throw:
- 4.5 stitches per inch x 6 rows per inch = 27 stitches per square inch
- 50 x 60 = 3,000 square inches
- 3,000 x 27 = 81,000 stitches
That number looks alarming and it is also the useful one, because it tells you the project's scale. It is also the reason a blanket takes weeks: 81,000 stitches at 30 stitches a minute is about 45 hours of plain working before finishing.
Step four: convert stitches to yarn
A plain worsted stockinette stitch consumes roughly 1.3 to 1.5 inches of yarn. Call it 1.36 inches as a working figure.
81,000 stitches x 1.36 inches = 110,160 inches, which is 3,060 yards, or about 15 skeins of 200 yards.
That is on the generous side of the commonly quoted 1,800 to 2,400 yards for this blanket, and the difference is real rather than an error: the lower figures usually assume a looser gauge, a lighter yarn, or that the blanket is smaller than 50 by 60. Treat the range as the answer and the single number as a starting point.
Step five: add the margin
Add 15 percent. Dye lots vary, borders use more than they look like they will, and running out at 90 percent of a queen size blanket is an expensive problem. Order one extra skein when you are near a boundary, and order the whole lot at once from the same dye lot.
The shortcuts, if you do not want to do the arithmetic
- Weigh as you go. Weigh your yarn cake before you start, note the weight, then weigh what is left when you finish a section. You now know exactly what that section cost in yarn, and you can extrapolate honestly.
- The half rule. A blanket needs roughly half as much yarn again as you think it does. This is not arithmetic, it is experience, and it is closer to right than most first estimates.
- Buy the border yarn separately. If the border is a contrast colour, buy it as a separate order rather than reducing the body order.
What to do with the answer
Take your skein count to the shop, check every skein carries the same dye lot, and buy them all. If the shop does not have enough, order the rest immediately rather than starting, because a second order may arrive from a different batch.