Blanket Size Calculator
A blanket finishes at the mattress size plus the drop over the sides, not at the mattress size. The width takes the drop twice, once at each side; the length takes it once, at the foot, because the top edge stops in front of the pillows. On a 150 × 200 cm bed with a 25 cm drop that is 200 × 225 cm, and at 16 sts per 10 cm the cast-on is 320 stitches.
Your numbers
Finished width
200cm
Finished length
225cm
Cast-on stitches
320sts
Formula
Finished width = Mattress width + 2 × Drop per side, Finished length = Mattress length + Drop per side
Holding 200 cm of stitches needs a circular needle of 100 cm or longer, and once the finished piece passes a kilo it stretches lengthwise under its own weight — measure your gauge swatch with that weight in mind. Baby blankets come from cot or car-seat dimensions instead: there should be no drop to hang over anything.
What to enter
| Input | Default | Accepted range |
|---|---|---|
| Mattress width (cm)The mattress across, measured on the mattress itself rather than over the bedding. | 150 | 30 and up |
| Mattress length (cm)The mattress head to foot, excluding the headboard. | 200 | 30 and up |
| Drop per side (cm)How far it hangs over the side; the width takes this twice, once each side. | 25 | 0 and up |
| Stitches per 10 cm (sts/10 cm)Stitches in 10 cm. If you measured over 5 cm, double it before entering. | 16 | 1 and up |
Step by step
Quick reference table
Results when only Mattress width (cm) changes and everything else stays put.
| Mattress width (cm) | Finished width (cm) | Finished length (cm) | Cast-on stitches (sts) |
|---|---|---|---|
| 75 | 125 | 225 | 200 |
| 113 | 163 | 225 | 261 |
| 150 | 200 | 225 | 320 |
| 225 | 275 | 225 | 440 |
| 300 | 350 | 225 | 560 |
What each result means
| Result | At default values |
|---|---|
| Finished width (cm)The width when finished, before any seam or fold allowance. | 200 |
| Finished length (cm)The length when finished. | 225 |
| Cast-on stitches (sts)Stitches to cast on; round to the pattern repeat. | 320 |
Common mistakes
Holding 200 cm of stitches needs a circular needle of 100 cm or longer, and once the finished piece passes a kilo it stretches lengthwise under its own weight — measure your gauge swatch with that weight in mind. Baby blankets come from cot or car-seat dimensions instead: there should be no drop to hang over anything.
Glossary
- Mattress width
- The mattress across, measured on the mattress itself rather than over the bedding.
- Mattress length
- The mattress head to foot, excluding the headboard.
- Drop per side
- How far it hangs over the side; the width takes this twice, once each side.
- Stitches per 10 cm
- Stitches in 10 cm. If you measured over 5 cm, double it before entering.
- Finished width
- The width when finished, before any seam or fold allowance.
- Finished length
- The length when finished.
- Cast-on stitches
- Stitches to cast on; round to the pattern repeat.
Frequently asked questions
Q. How is Blanket Size Calculator calculated?
Finished width = Mattress width + 2 × Drop per side, Finished length = Mattress length + Drop per side — A blanket finishes at the mattress size plus the drop over the sides, not at the mattress size. The width takes the drop twice, once at each side; the length takes it once, at the foot, because the top edge stops in front of the pillows. On a 150 × 200 cm bed with a 25 cm drop that is 200 × 225 cm, and at 16 sts per 10 cm the cast-on is 320 stitches.
Q. Can you walk through an example?
With Mattress width 150cm, Mattress length 200cm, Drop per side 25cm, Stitches per 10 cm 16sts/10 cm, the answer is Finished width 200cm.
Q. What do I need to enter?
Enter Mattress width, Mattress length, Drop per side, Stitches per 10 cm. The result recalculates as you type, and an empty box counts as zero.
Q. How much does the answer move if I change a number?
Changing only Mattress width (cm) moves the answer to Mattress width (cm) 75 → Finished width (cm) 125 and Mattress width (cm) 300 → Finished width (cm) 350. The table below lays out five steps.
Q. How are the numbers rounded?
Money is shown to the nearest whole unit, percentages to one decimal place and everything else to two. What you see is rounded; the calculation itself carries the unrounded value forward.
Q. Anything to watch out for?
Holding 200 cm of stitches needs a circular needle of 100 cm or longer, and once the finished piece passes a kilo it stretches lengthwise under its own weight — measure your gauge swatch with that weight in mind. Baby blankets come from cot or car-seat dimensions instead: there should be no drop to hang over anything.
Related calculators
Materials differ in density and absorption. If your label states a figure, use it — the defaults here are only common values.