Wool amount

[Ritz]

How do you know how many balls of wool you would need to buy for a blanket that is 50" by 70" for this pattern

 

[Avon Lady]

Do you have the written copy of this pattern?  It should tell on it how many ounces you will need.

[Ritz]

The pattern is for a HAT and the friend wants the pattern for a blanket

[Ritz]

I am using Barnett Pop! for the HAT I am able to  make 2 hats adult from the wool.  It is a 5 oz ball

[redrosesdz]

Get some of the yarn you plan to use. Make a swatch 5"x5", using the hook and pattern that you plan to use.

To get the amount of yarn, weigh the swatch. That will tell you how much yarn in 25 sq. Inches (5x5). Multiply the weight by 140 to get the amount needed for 50"x70". (Or measure the length you used and multiply it by 140. Weight is easier.)

To calculate your starting chain, measure the middle 4" across of the swatch. Count the number of pattern repeats or stitches. Multiply the number by 12.5 for 50". Round up.

To calculate your row count, measure the middle 4" vertically. Count the rows. Multiply that by 17.5 for 70". Round up.

The reason you measure the middle is because edges are unreliable. 

[Granny Square]

^ That's the most accurate (making a swatch).  However, it's do-able to measure the yardage if you haven't invested in a postal scale.  Unravel the swatch, dump it on the floor, hold a yard stick vertically (so it doesn't fall off), pick up an end of the yarn and wrap it around the yardstick end to end , counting yards as you go.  Don't pull it really tight.  

And yeah, I second rounding up.  SO many times a pattern calls for x skeins, and I buy x+1 and need to break into that 'extra' skein to finish the last few rows.  It works out in the end, I just finished a holiday gift using a couple of those 'slighly broken into' skeins from earlier projects.