Help with measurements!
 

I am attempting to figure out the measurements for a Double Irish Chain quilt.

The plain center square, coffee cups and pots, measures 8 1/4" unfinished.
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I thought my squares should be 2.5" but it doesn't work out, center block measures 12". How do I figure out, what I should add to the center square and what size squares should I be cutting for the other block??
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Thanks in advance, before I have to go buy more fabric because I cut it all wrong!!!!!

If your squares finish at 2.5 your pieced blocks will be 12.5 finished. If you change your borders to 2.5 finished you would need to trim your center pieces all the way around to give you 7.5 center finished and 5 inch total borders for the 12.5 to match your pieced block

I am not good at math, so I would draft out on graft paper and then measure the parts.

Agree with cjsews. Try cutting your sashing and squares at 3" and trim 1/4" off the centre blocks.

I am attaching a scan with some suggested measurements - for cut sizes and the theoretical finished size using 1/4 inch seams.

For block 1: - Unfinished size - 10-1/2 x 10 -1/2; finished size - 10 x 10

Piece 1A - Cut size - 2-1/2 x 2-1/2; finished size - 2 x 2
Piece 1B - Cut size - 2-1/2 x 6-1/2; finished size - 2 x 6
Piece 1C - Cut size - 6-1/2 x 6-/12; finished size - 6 x 6

Block 1 - Unfinished size - 10-1/2 x 10-1/2; finished size - 10 x 10

Block 2: - Unfinished size - 10-1/2 x 10-1/2; finished size - 10 x 10

All pieces use the 1A piece - 2-1/2 x 2-1/2; finished size - 2 x 2

Block 2 - unfinished size - 10-1/2 x 10-1/2; finished size 10 x 10

For a block with an unfinished size of 13 x 13; finished size of 12-1/2 x 12-1/2;

Cut piece 1A - 3 x 3 - finished size 2.5 x 2.5
Cut piece 1B - 3 x 8 - finished size 2.5 x 7.5
Cut piece 1C - 8 x 8 - finished size 7.5 x 7.5

Block 2 - all pieces are the same size as 1A - 3 x 3


For a block that finishes at 7.5 x 7.5 - unfinished size 8 x 8

Cut 1A - 2 x 2; finished size 1.5 x 1.5
Cut 1B - 2 x 5; finished size 1.5 x 4.5
Cut 1C - 5 x 5; finished size 4.5 x 4.5

All the pieces in Block 1 - cut 2 x 2 ; finished size 1.5 x 1.5


One can go to 1/4 inch increments -

block would finish at 11.25 x 11.25:
piece 1A - cut at 2.75 x 2.75 -
piece 1B - cut at 2.75 x 7.25
piece 1C - cut at 7.25 x 7.25

block would finish at 8.75 x 8.75:
piece 1A - cut at 2.25 x 2.25 -
piece 1B - cut at 2.25 x 5.75
piece 1C - cut at 5.75 x 5.75
piece 1A - cut at 1.75 x 1.75 -

block would finish at 5 x 5:
piece 1A - cut at 1.5 x 1.5 -
piece 1B - cut 1.5 x 3.5
piece 1C - cut 3.5 x 3.5

If you want to use the center as cut size 8-1/4, and use a 5 x 5 grid, then the cut size of the pieces should be:

1A: 3.08 x 3.08
1B: 3.08 x 8.25
1C: 8.25 x 8.25

The block would finish at approximately 12.91x 12.91 inches - 13.41 x 13.41 unfinished

These are not "impossible" numbers to work with - just a bit unconventional for most people used to working with 1/8.

I would suggest either sashing the coffee pieces to make them a bit bigger, or cut them down.

I would consider "shaving" the 8.25 x 8.25 piece to 8 x 8-

Cut 1A - 3 x 3
Cut 1B - 3 x 8
Cut 1C - 8 x 8

Finished size will be 12.25 (2.5 + 7.5 + 2.5 = 12.5)

I always get my graph paper out and figure my measurement of blocks that way but it looks like you are getting some tremendous help here. I am definitely not a math person so graph paper is my answer.

Bearisgray - you're so very generous and helpful! Love your thought process and appreciate your math :) If there's a will there's a way, right?