Quick answer: how to calculate block size and layout
Blocks across equal target width divided by finished block size, rounded to the nearest whole block, and blocks down equal target length divided by finished block size, rounded to the nearest whole block. Total blocks equal blocks across times blocks down. Finished quilt size equal blocks across times block size, by blocks down times block size, which can differ from target size when target size is not an exact multiple of block size. Unfinished block size equal finished block size plus 0.5 inches, for 0.25 inch seam allowance on each side, and layout uses finished size, never unfinished size.
Example: target 58 by 76 inches, block 9 inches. Blocks across are 6, blocks down are 8, total blocks are 48, finished size is 54 by 72 inches, which is 4 inches smaller than target in both directions. Larger layout is 7 by 9 blocks, 63 blocks, finished 63 by 81 inches. Choose nearest, smaller, or larger, or bridge the difference with a border, but do not stretch blocks to force the target size.
Scope, stated plainly: this calculator handles straight-set square blocks only, with no sashing and no borders. It does not handle rectangular blocks, on-point layouts, sashing, or borders. For sashing, use the Sashing Calculator, and for borders, use the Border Calculators, after the block layout is fixed. For an on-point layout, a straight-set count cannot be reused, because a rotated block spans block size times 1.414, not block size.
If you only need a number, use the Block Size Calculator. If you want to understand why finished size shifts, read on.
What block size and layout mean
Block size means the size of one block in the finished quilt, after seams are sewn. Layout means how many blocks fit across the quilt top, how many blocks fit down the quilt top, and how many blocks there are in total. Block size and layout together give finished quilt size, which may differ from target quilt size.
Target quilt size is the size you want, before you choose blocks. Finished quilt size is the size you actually get, from blocks you actually sew. If target size is an exact multiple of block size, finished size equals target size. If target size is not an exact multiple of block size, finished size differs from target size, and you must choose a layout, or add borders or sashing, to reach target size.
Finished size versus cut size
| Size | Meaning |
|---|---|
| Finished size | Size in the finished quilt, after seams are sewn |
| Cut size | Size as cut, before seams are sewn, including seam allowance |
Block finished size is used in layout calculation, not cut size, because layout is about the finished quilt, not about cutting. For example, a 12 inch finished block is cut larger, with seam allowance on each side, but it measures 12 inches in the finished quilt, and it counts as 12 inches in layout. Using cut size in layout would give too few blocks, because cut size is larger than finished size.
Step by step: how to calculate block size and layout
Step 1: Work out blocks across and blocks down, nearest layout
Blocks across, nearest layout, equals target quilt width divided by block finished size, rounded to the nearest whole number. Blocks down, nearest layout, equals target quilt length divided by block finished size, rounded to the nearest whole number. For target width 58 inches and block size 9 inches, blocks across equals 58 divided by 9, equals 6.44, rounded to the nearest whole number, equals 6 blocks. For target length 76 inches and block size 9 inches, blocks down equals 76 divided by 9, equals 8.44, rounded to the nearest whole number, equals 8 blocks.
Step 2: Work out total blocks and finished quilt size, nearest layout
Total blocks equals blocks across times blocks down. For blocks across 6 and blocks down 8, total blocks equals 6 times 8, equals 48 blocks. Finished quilt width equals blocks across times block finished size. Finished quilt length equals blocks down times block finished size. For blocks across 6, blocks down 8 and block size 9 inches, finished quilt size equals 54 by 72 inches.
Step 3: Work out smaller layout and larger layout
Smaller layout rounds blocks across and blocks down to whole numbers, and gives a smaller finished size than target size, unless target size is an exact multiple of block size. Larger layout rounds blocks across and blocks down up to whole numbers, and gives a larger finished size than target size, unless target size is an exact multiple of block size. For target 58 by 76 inches and block size 9 inches, smaller layout equals nearest layout, 6 by 8 blocks, because both fractions are less than 0.5, so rounding to the nearest whole number is the same as rounding down. Larger layout equals 7 by 9 blocks, total 63 blocks, finished size 63 by 81 inches.
Step 4: Choose a layout, or add borders or sashing
Choose the layout whose finished size is closest to your target, or add borders or sashing to reach your target size. For target 58 by 76 inches and nearest layout finished size 54 by 72 inches, you are 4 inches short in both width and length. A 2 inch border on each side, on all four sides, would add 4 inches in width and 4 inches in length, and reach target size exactly, before border seam allowances are counted in finished border width.
Try it with the calculator: Use the Block Size Calculator with your own target quilt width, target quilt length and block finished size. It uses the same steps as this guide, and it shows nearest layout, smaller layout and larger layout, together.
Worked example: target 58 by 76 inches, block 9 inches
Take target quilt size 58 by 76 inches, block finished size 9 inches.
Blocks across, nearest layout: 58 divided by 9 equals 6.44, rounded to the nearest whole number, equals 6 blocks. Blocks down, nearest layout: 76 divided by 9 equals 8.44, rounded to the nearest whole number, equals 8 blocks.
Total blocks, nearest layout: 6 times 8 equals 48 blocks.
Finished quilt size, nearest layout: 6 times 9 equals 54 inches wide, 8 times 9 equals 72 inches long, so finished quilt size equals 54 by 72 inches.
Smaller layout: blocks across 6, blocks down 8, total 48 blocks, finished size 54 by 72 inches, same as nearest layout. Larger layout: blocks across 7, blocks down 9, total 63 blocks, finished size 63 by 81 inches.
In this example, nearest layout finished size 54 by 72 inches is 4 inches smaller than target size in both width and length. Larger layout finished size 63 by 81 inches is 5 inches larger than target size in both width and length. Nearest layout is closer to target size than larger layout, by 1 inch in each direction, so nearest layout is the better choice, unless you want a larger quilt.
Finished versus unfinished table, and layout table, our own computed tables
Finished to unfinished, with 0.25 inch seam allowance per side: 6 inches finished cut at 6.5 inches, 9 inches finished cut at 9.5 inches, 10 inches finished cut at 10.5 inches, 12 inches finished cut at 12.5 inches. Label both numbers every time, finished for layout, unfinished for cutting, and never mix them in one calculation.
| Finished block size | Blocks for a 60 by 60 in target, nearest layout | Finished size, nearest layout |
|---|---|---|
| 6 in | 10 by 10, 100 blocks | 60 by 60 in |
| 9 in | 7 by 7, 49 blocks | 63 by 63 in |
| 10 in | 6 by 6, 36 blocks | 60 by 60 in |
| 12 in | 5 by 5, 25 blocks | 60 by 60 in |
Notice that a 9 inch block does not divide 60 inches evenly, so the nearest layout grows to 63 inches, it does not shrink blocks to 8.57 inches. Block size stays fixed, finished size shifts, or a border bridges the gap.
How to make sure your result is correct
- Finished versus unfinished check. Layout must use finished size, cutting must use unfinished size, which is finished plus 0.5 inches. Using unfinished size in layout overcounts blocks.
- Rounding check. Blocks across and down must be whole blocks. Nearest layout rounds to the nearest whole block, smaller layout rounds down, larger layout rounds up, and all three must be shown before choosing.
- Finished size check. Finished size must equal blocks across times block size, by blocks down times block size, not target size, when target size is not an exact multiple.
- Square and straight check. This calculation is for straight-set square blocks only. Rectangular blocks, on-point layouts, sashing, and borders need their own calculations.
- Border bridge check. If finished size differs from target size, bridge the difference with a border, or accept the nearest size, never stretch blocks to force target size.
Common mistakes with block size and layout
- Using cut size in layout. Cut size is larger than finished size, because cut size already includes seam allowance. Using cut size in layout gives too few blocks, and a finished quilt smaller than planned. Use finished size in layout, not cut size.
- Rounding blocks up without checking. Rounding blocks up gives a larger finished size than target size, which may be too large. Always check smaller layout, nearest layout and larger layout, and choose the layout whose finished size is closest to your target.
- Forgetting sashing and borders. This calculator assumes square blocks, with no sashing between blocks, and no borders added. If you want sashing or borders, work out block layout first, then add sashing or borders with the Sashing Calculator or the Border Calculator.
- Assuming finished size equals target size. Finished size equals target size only if target size is an exact multiple of block size. If target size is not an exact multiple of block size, finished size differs from target size, and you must choose a layout, or add borders or sashing, to reach target size.
Calculate your own block layout now
Use your target width, target length and finished block size in the calculator, and check the result against the steps in this guide.
Open the Block Size CalculatorFrequently asked questions
Divide target quilt width by block finished size and round to the nearest whole number to get blocks across, divide target quilt length by block finished size and round to the nearest whole number to get blocks down, then multiply blocks across by blocks down to get total blocks. For example, target 58 by 76 inches and block 9 inches gives 6 blocks across, 8 blocks down, and 48 blocks total.
Block finished size is the size of one block in the finished quilt, after seams are sewn, not the cut size. For example, a 9 inch finished block is cut larger, with seam allowance on each side, but it measures 9 inches in the finished quilt.
Then finished quilt size will differ from target size. The smaller layout rounds blocks down and gives a smaller finished size, the larger layout rounds blocks up and gives a larger finished size, and the nearest layout rounds blocks to the nearest whole number. Choose the layout whose finished size is closest to your target, or add borders or sashing to reach your target size.
Use finished size in layout, not cut size, because layout is about the finished quilt, not about cutting. Cut size is larger than finished size, because cut size already includes seam allowance. Using cut size in layout gives too few blocks.
No. This calculator assumes square blocks, with no sashing between blocks, and no borders added. For rectangular blocks, work out blocks across and blocks down separately, with block width and block length, or use the Sashing Calculator for sashing between blocks.
Related guides and calculators
Next, read How to Calculate Quilt Sashing for the strips between blocks, and use the Sashing Calculator for sashing between your blocks. For the layout itself, use the Block Size Calculator.