I keep noticing this search term pop up in hits on my blog, (OK the second term, not the first) so I thought I’d take time out to answer it.
Sadly, the answer is, there is no easy answer. But what’s most important to remember is that, if you make a simple granny square, each round will take more yarn than the last.
If you want to estimate how much a round will take you, you need to do a little prep work. Firstly, you need some electronic kitchen scales – the kind than measure grams or ounces (OK, I didn’t say it was going to be easy!).
Weigh your square. Then crochet one full round (ie four sides of the square). Weigh it again. The difference is the weight of the yarn you just used. Write that down.
Then work another full round. Weigh your square again. The difference now is the weight of the second round you made. Write that down too.
Now compare the weights of the yarn you used on each of the two rounds.
If you want to be exact in predicting how much more you’ll need each round, you need to work out the relationship between the two. For example, if the first round took 10g, and the second round took 10.5g, then you used 5% more yarn for the second round. This is roughly how much your round will grow each time.
So your next round will take about 105% of 12g, which is 11.025g (Work is out by doing the calculation 10.5 x 1.05). Your next round should take about 105% of 11.025g, which is 11.57g (11.025 x 1.05).
Keep going and you should be able to work out how much yarn you need for each round. If you just change colours but use the same type of yarn it’ll be pretty accurate. But if you’re changing weights of yarn, then it’s not. This technique only works if you stick to the same weight (and heck, the same brand and type) of yarn.
Not got any scales? You can also work a whole round, unravel it and measure the length of the yarn you just used. But that will only give you the amount needed for that round. Again, you’d need to work 2 rounds, unravel both and measure them and compare the two to get an idea of how much more you’ll need as the square gets bigger and bigger.
But the bottom line is, none of this really matters. Honest. The idea is to get rid of itty bits of your stash. Just go with the flow, use up whatever yarn you can get your hands on, and keep going round and round in circles until you get sick of it!
My giant granny square is now so big it takes 30g per double stripe. Pretty soon I’ll have to switch to single rounds, and I think when it gets to the point that it takes a whole ball to do a single stripe I’ll just stop. Because the point of all this is usually to not buy more yarn. Ahem.