Because I mostly knit baby stuff , I have the patterns written in baby sizes. To transform a baby blanket into an afgan or a big blanket, it is easy to calculate how many stitches to cast on to make a certain size. But then comes the question: how much yarn to buy???

Most of the skeins have the weight on them, so my calculations are based on this.

Well, my dears, this is when we need a bit of math … oh, no! don’t run away! I promise that is quite simple.

I am using the metric measurements, but even if you use the imperial, the logic is the same.

What do we need? A scale. An electronic one, is more accurate, so, it is better.

Don’t forget that the calculations are more for orientation, but this is what I use.

First knit your swatch. Mine was 15 x 8 cm and was weighing 8 grams.

The area of the swatch is: 15*8cm = 120 square cm

If 120 sq cm weighs 8 grams

Then 100 sq cm weigh…”z” grams

—————————–

“z” = 100*8 / 120 = 6.66 grams per 100 square centimeters

This means that an area of 100sq cm will weigh about 6.7 grams. (Aproximatelly)

Examples:

**Let’s say I want to knit an 100cm x 150 cm afghan. **

**It will have an area of: 100*150 = 15000 sq cm. **

** Quantity of yarn: aprox 6.7 g * 150 = 1005 grams (We multiply with 150 because 6.7 grams are for 100 sq cm)**

** That will be 10 skeins of 100 grams each.** **OR 5 skeins of 200 grams each. or what ever yarn you decide to use. **

*Let’s say I want to knit a 75*110 cm crib blanket*

*Area: 110*75 = 8250 sq cm*

*Quantity of yarn: 6.7 g * 82.5 = 552.75 grams*

*That will be almost 6 skeins of 100 g each*

*Or 11 skeins of 50 grams each*

I am so curious of what you think of this. Do you fond it helpful? What did you used it on (if you did)