Please help me with my math
 

I'm getting ready to order fabric for sashing my first large project and I want to make sure I have enough. Can you please check my math?

I'm making 80 4" squares, and I want 2.5" sashing around each block. I'll be using cornerstones, too.

So I figure 4 sides x 80 squares = 320 4" strips = 1280" of strips

1 yard of fabric = 560" of 2.5" strips

1280/560 = 2.3

So 3 yards is WAY more than enough, right?

Oh, and I figure for 8 x 10 rows I'll need 90 cornerstones.

Thanks for helping. I really want to get this right the first time!

Are you putting sashing on the edges? Or will you have a border?
Usually you add sashing to the right and bottom of each block.
Then add to the top and sides if that's what you want or put a
border all around. If you add sashing on all four sides you will
end up with double sashing. Here's a link to help you. Draw it
on graph paper then count how many sashings you need.
http://www.synthcom.com/~val/Quilts/...ngSashing.html

EasyPeezy has given you good advice - you won't put sashing around 4 sides of each block. Nothing is what it seems!!

Are you putting sashing on the edges? Or will you have a border?
Usually you add sashing to the right and bottom of each block.
Then add to the top and sides if that's what you want or put a
border all around. If you add sashing on all four sides you will
end up with double sashing. Here's a link to help you. Draw it
on graph paper then count how many sashings you need.
http://www.synthcom.com/~val/Quilts/...ngSashing.html

You might want to arrange your blocks before you add your sashing
because some will need sashing just on some sides and not all around.

See? I knew I needed help! Back to the graph paper!

ok, now I got 90 strips for l/r sides of blocks = 360"
88 strips for top/bottom of blocks = 352" total 712"

so 2 yards of fabric should be plenty. Unless I'm still wrong.

Should be just fine.:thumbup:

Thank you!

Not to throw a monkey wrench into the works, but sashing around all 4 sides of the block is exactly how I do it. That way all I have to do is sew the finished blocks into rows and match the seams at the corners. Takes the headache out of making sure the rows all line up perfectly on long rows of sashing.

Yikes! Monkey wrench! I might order extra fabric just in case. Boy, this stuff is complicated!

Too.Many.Numbers...I'm so glad there are others here that aren't put off by the math portion of quilting!

But when you do this I would have to think that you must reduce the width of your sashing strips to half of what you would use if sashing in the more tradtional aspect. In the OP's example surely she would not sash 4" blocks with 2" (finished) strips on all 4 sides, That would make the finished size of the sashing the same size of the blocks completely defeating the look of sashing and making it look more like alternate unpieced blocks.

So I think she is still quite safe with 2 yards of fabric for the sashing whichever way she decides to sash. IMHO when doing corner stones it is very easy to line the strips up when assembling the quilt. Order an extra yard just to be safe or in case she decides to use the sashing fabric as binding as well.

Here's I do the math:

for a 8 x 10 layout with sashing going around the outside
9 vertical sashing strips per row X 10 rows = 90 vertical sashing strips
11 horizontal rows of sashing (includes the top/bottom outside edges) x 8 strips / row = 88 horizontal sashing strips
90 vertical + 88 horizontal = 178 sashing strips needed.

Is the 4" square finished (cut at 4 1/2") or unfinished (finishes at 3 1/2")?

Assuming that the 4" square is the finished size (cut at 4 1/2"):
Each sashing strip needs to be cut at 4 1/2" x 2 1/2". You can typically get nine 4 1/2" strips per width of fabric (assuming usable width of fabric is at least 40.5").
178 strips / 9 strips / wof = 19.77777 --> so 20 wof are needed to cut the 178 sashing strips.

Each sashing strip needs to 2 1/2" wide (assuming 2 1/2" is the unfinished measurement and they are finished at 2")
2 1/2" / wof * 20 wof = 50" of sashing fabric needed to cut 20 strips at 2 1/2", with each strip making nine 4 1/2" x 2 1/2" sashing pieces.

50" / 36" / yd = just a tiny smidge over 1 3/8 yard, so get a minimum of 1 1/2 yards of sashing fabric

As for the cornerstones, you will need 99, not 90. (11 rows of horizontal sashing with 9 cornerstones per row).
At 2 1/2" cut size, you can typically get 16 squares per WOF (assuming at least 40"). You need 7 rows of fabric to cut the 99 squares. At 7 rows of fabric by 2 1/2" in width, you need just a smidge under 1/2 yard, which I would round to 5/8 yard cornerstone fabric.

Good luck!

This is true - she would reduce the width of her sashing. I wasn't debating the amount of fabric, I was simply stating there is more than one way to skin a cat, i.e., add sashing to a quilt.

Wow, thank you! That's so helpful!