How much yarn? I can't work it out .. durrrrr

[SaaraGH]

Hi All, I want to make a blanket most likely in Aran weight yarn for a king size bed 81x81 ins. Looking at Caron Cakes or Caron Simply soft. I'm getting drastically different amount each time I work it out. The blanket will either be a C2C or some other solid pattern so minimal holes in it. Can anybody help please?

[redrosesdz]

Welcome to Crochetville! 

There's a big difference between CC and CSS yarn. CC is on the thicker side of worsted weight yarn and CSS is thinner than most worsted. For dense stitches, I'd use a K or L for CC and a 7 or H for CSS. This means that it takes a lot more CSS to make something that huge. Then there's the weight of the finished product. CSS is heavier per gram. The biggest afghan I've made out of CSS is a couch size throw and it's a couple of pounds. A king size afghan in dense stitches is going to be heavy, no matter which yarn. I recommend picking yarn that is lighter per gram.

Here's how to determine how much yarn and how much the final product will weigh...

Pick yarn, pattern and hook. Make a swatch that's 4" or 5" square. Weigh it to calculate the final weight. You can use the weight to calculate how much yarn you'll need, too. (Grams are more accurate than oz.) If you prefer buying yarn by length, mark the end with a stitch marker between the strands or a small piece of tape. Unravel the swatch. Measure the amount of yarn used to calculate the length you'll need. When making something big, I buy an extra skein to be safe.

Here's a link for afghan sizes. It includes a yarn calculator. There are other sites that have slightly different sizes, too.

http://thecrochetcrowd.com/afghan-sizes/

[Granny Square]

Interesting, thanks for that link I hadn't seen that one before with the yarn estimates--but I couldn't find any real calculators, just generic chit chat and links that went in circles (probably my operator error...).

I have another thought, or double-check the calculation by weight - try to calculate the yardage.  A gram is a really tiny weight measure (28+ grams in an ounce) and I doubt most of us have scales that measure grams.  Take that swatch (the bigger the better for accuracy), measure it and calculate the area in square inches - including fractions.  Now, unravel it and measure the yardage (wrap it loosely around a yardstick end to end, longwise).  Figure out the yardage per inch - use the fractions and if anything round up in the fraction of yard per inch.

You want a blanket 81x81, so 6561 square inches.  Take your yardage per inch and multiply it by 6561 - that's how much yardage you need.  Round up when buying skeins.

Another way, very 'ballpark', is to look at similar afghan pattern yarn requirements and extrapolate.   Example:  you mentioned corner to corner, here is a pattern for a 67x67 blanket that takes 4984 yards. 67x67 is 4489 square inches, so 4984/4489 is 1.11+ yards per inch.  So, if your gauge is spot on with the designer of that blanket, you'd need ~7285 yards.

Yarn weight classifications are a range, which is why you'll see US #4 weight yarn brands have a very slight variations in weight and also wraps per inch.  If you choose a yarn which seems thinner/more wraps per inch in the same yarn range, you are likely need more yardage.  US #4 weight is 9-11 wraps per inch, DK is 12-14 for example.