A yard in each color should do.
This is how I do the math.
180squares/4(colors)= 45 squares per color.
I usually use 40" as width. So, 40"/5"= 8 squares.
Which means you can get 8 squares on a 5" strip (selvage to selvage).
Now you calculate how many strips you need to make 45.
45/8=5.6 round this up to 6. So 6 x 5"=30" which is 30/36= 0.83 yard
which you round up to 1 yard and you get a little extra for stash or insurance. See?

I just buy alot of each fabric and if I am using a color that I'm using alot to be dominate. I double the amount of it...and Yes its a stash builders method...but thats okay with me

go to joanns with a 40 or 50 percent coupon and buy the fabri-calc. it really works.

Or if you have an iPhone they have several free apps that allow you to calculate :) but with either option you do have to have an idea of what your finished product will be and like someone said on here, I rarely buy fabric specifically for a project ... My projects normally pick from my fabrics :)

I usually eyeball it, and over purchase. The fabric calc is a good suggestion. I'm assuming you don't have Electric Quilt or another design program...it's just another benefit if you do because you can draw up your quilt before hand in the exact size and it will figure yardage for you.

4 different colors doesn't have to mean 4 different fabrics.

Why can't it be 5 different fabrics of the same color/value? But the texture of the prints is different, giving some life to the pattern. So you're using 20 different fabrics. It really doesn't cost much more as your buying FQ's instead of yardage.

And this way you never "run out" of a particular fabric. If you're short because you want more blocks, you just buy another FQ of the same color. As long as they're spread out on the quilt top, it will look fabulous.

And it always makes for a much more interesting quilt.

Heh. It's pretty rare that I buy fabric for a plan in mind. I buy the fabric and then make up a plan based on what I have when I start pulling from my stash. LOL

This is REALLY cool!
David
http://vrya.net/quilt/classic.php

And here's another calculator. :)
http://www.blockcentral.com/calculators.shtml

The quilter's pocket reference by Peggy Scholley is great for a yardage reference.