I was in the process of answering this question but hit the wrong button and lost it so will begin again.

Back in the olden days of the 1970's before all the new technology was avaiable we calculated as follows.

Take the block
Determine where each fabric or color will be
Measure each piece and calculate square inches adding seam allowances.
Multiply that by the number of times that fabric will be used in the block
Calculate square inches in a yard (36"x42") is 1512 square inches. It is probably safe to use 42" as a standard.
Divide your needs by the square inches in a yd or 1512.

Example using a Rain Fence and using only 3 fabrics.

The block will finish at 9"
Requires 3 bands which finish at 3"x9"
Add your 1/2" to length and width or a cut piece of 3.5"x9.5"

Finished quilt will be about 64"x90"

64 divided by 9 - 7.1 So the decision is to make it 7 blocks wide for a finished quilt of 63 or up it to 8 blocks. Lets keep it at 7

90 divided by 9 = 10 blocks long.
Total number of blocks will be 70. (7x10)

Now each bar in the blocks is to be cut at 3.5"x9.5" or 33.25 square inches x 70 (blocks) = 2327.5 square inches of each color.

2327.5 divided by 1512 = 1.539 yds of each color
or a little over 1 1/2 yd of each color.

Then plus what you might need for borders and binding.

Now if you put a 3" finished border on the quilt you:

Measure around the quilt which is 64 x2 plus 90 x2 is 308 inches. If your fabric is 42" wide and you are cutting on the width of the fabric you will divide 42" into 308 which gives you 7.3 (or 8 strips)
The border will be cut 3.5" wide so 3.5x8 strips is 28" additional
The quilt now becomes 6" larger so
64 plus 6" is 70
90 plus 6 is 96 and the perimenter is now 320 inches

320 divided by 42 is 7.6 or 8 strips
Binding is cut 2.5" times 8 = 20 inches for binding.

Then always add a bit for miscutting.

Not I should be cutting kits for my upcoming classes and should not be spending time doing this but got into a roll.
Hope this doesn't bore anyone. And hopefully the math students will send me a private message and tell me where I am wrong......lol
I know there are all kinds of devices to do this but some don't have have such electronic wizards. I don.t

So for those who might need to do this in the middle of the night and not time to search and search and search, this is how it is done.

Thanks for that! That's what I've been thinking about, actually, so you've saved me some noodling!

thanks for this information!

All good information. It's amazing how easy it is for us oldtimers. I haven't bought many patterns, so I find myself doing this often, though I am not as detailed as you in the strips for the block. :thumbup:

where did the 1512 number come from that yiu divided into 2327.5? I am lost here.

I went back and reread it , then I saw the answer to my question. thanks

The 1512 represents the square inches in one yard of 42" fabric. (36"x42" = 1512 square inches. Say my calculations indicate I need 3000 square inches then I will divide the 1512 into 3000 and get 1.98 yds or 2 yds.

In these calculations you work with square inches and then convert to yardage.