|This is a post I wrote for the message boards to answer the question: "I want to make a queen size quilt made entirely of 4" squares. How many squares do I need?"
First, you need to decide what size to make the quilt. According to some notes I have from a quilt book, a queen size quilt is about 84"x92"; my Lands' End catalog says their queen size quilts are 96"x98" - so somewhere around those sizes. A lot depends on how much you want it to hang down on the sides (half way with a bed skirt, or to the floor) and whether it goes over the pillows (and tucks under them). If you quilt heavily the quilt can shrink up a bit, so it's better to plan to make it an inch or two larger just in case.
Let's go with 84x92. To get the number of 4" squares, divide each dimension by 4. That gives 21 squares across, 23 squares down for a grand total of 21x23 = 483 squares. Having an odd number of squares in a row is usually desirable - it just looks more balanced - but once it's on the bed it really doesn't matter. You can just sew these together and bind it without any kind of border, or add a plain 1" or 2" strip around the outside as a simple border. I think the border helps stabilize the quilt top before you go to quilt it, but it's a personal decision. If you use a 2" border you could eliminate one row and one column of squares (20x22 = 440 squares).
To cut the squares, you'll cut a 4.5" strip of fabric (.5" for the seam allowances!) and then cut that into 4.5" squares. Although quilting fabric is supposed to be 45" wide, it's often less especially if you preshrink; plus you'll be cutting off the selvages. I usually plan on 42" wide, which is 21" wide when it's folded. You'll get 21/4.5 = 4 squares out of one thickness, which means 8 squares out of a double thickness. You'll probably be able to squeeze one more square out of the folded piece that's left over, but to be safe don't count it in the total.
OK, that means that to get your 483 squares, you'll need to cut (483/8 = 60.375, round up to 61) 61 strips of fabric. This can be 61 different fabrics or 20 different fabrics, or just a few - it's up to you! You'll need at least a quarter yard of each fabric to get one strip (or cut two strips from a fat quarter). Of course you can cut individual squares from scraps, too.
If you're going to be using a limited number of fabrics, here's how to calculate the yardage to buy. Let's say you'll be choosing 8 fabrics. 61/8 = 7.625 strips of each fabric, round that up to 8 strips. 8x4.5 = 36" of each fabric, which is exactly a yard. Don't buy a yard - by the time you preshrink and straighten the ends, it won't be enough. Get either 1.25 or 1.5 yards of each fabric just to be safe. This also gives you a little extra, in case of cutting mistakes(!). Personally, I like to use a lot of different fabrics and I go ahead and cut a full strip of each fabric even if it means I have extra squares at the end. When you start to arrange the squares you may find that one fabric doesn't work as well as the others and you can just leave it out.
Don't cut the binding, or the border if you decide to have one, until the quilt top is assembled. By the time everything is sewn together it probably won't be exactly the right size (this is true for all of us!), so just measure the finished size and cut the borders to match.