15 Inch Quilt Block: Cut Sizes, Grids and How Many Blocks per Quilt
A 15 inch finished quilt block is cut 15 1/2 x 15 1/2 inches before sewing, which includes a 1/4 inch seam allowance on every side. It divides evenly into a four patch (2 x 2), nine patch (3 x 3), 4 x 4 grid, 5 x 5 grid, 6 x 6 grid. A 90 x 95 inch queen quilt needs 6 x 6 = 36 blocks with no sashing.
Quilt block sizes are always given as the finished size, the part you see once the block is sewn into the quilt. A 15 inch block is pieced and trimmed to 15 1/2 inches, then loses 1/4 inch on each side to the seams that join it to its neighbors.
What size do you cut the pieces for a 15 inch block?
Most traditional blocks are built on a grid. Divide 15 inches by the number of grid units to get each unit's finished size, then add 1/2 inch for squares or 7/8 inch for two-at-a-time half square triangles. Grids marked "awkward" land between eighth-inch marks on the ruler.
| Grid | Unit finishes at | Cut squares | Cut HST squares | Ruler friendly |
|---|---|---|---|---|
| Four patch (2 x 2) | 7 1/2 in | 8 in | 8 3/8 in | Yes |
| Nine patch (3 x 3) | 5 in | 5 1/2 in | 5 7/8 in | Yes |
| 4 x 4 grid | 3 3/4 in | 4 1/4 in | 4 5/8 in | Yes |
| 5 x 5 grid | 3 in | 3 1/2 in | 3 7/8 in | Yes |
| 6 x 6 grid | 2 1/2 in | 3 in | 3 3/8 in | Yes |
How many 15 inch blocks do you need for each quilt size?
Blocks across and down are rounded to the nearest whole block, so the finished top lands close to the typical quilt size. Sashing is the strip of fabric between blocks; with 2 inch finished sashing you need fewer blocks for the same size.
| Quilt | Typical size | No sashing | Top size | With 2 in sashing | Top size |
|---|---|---|---|---|---|
| Baby | 40 x 40 | 3 x 3 = 9 | 45 x 45 | 2 x 2 = 4 | 32 x 32 |
| Crib | 36 x 52 | 2 x 3 = 6 | 30 x 45 | 2 x 3 = 6 | 32 x 49 |
| Lap | 45 x 60 | 3 x 4 = 12 | 45 x 60 | 3 x 4 = 12 | 49 x 66 |
| Throw | 50 x 65 | 3 x 4 = 12 | 45 x 60 | 3 x 4 = 12 | 49 x 66 |
| Twin | 68 x 90 | 5 x 6 = 30 | 75 x 90 | 4 x 5 = 20 | 66 x 83 |
| Twin XL | 68 x 95 | 5 x 6 = 30 | 75 x 90 | 4 x 6 = 24 | 66 x 100 |
| Full / Double | 83 x 90 | 6 x 6 = 36 | 90 x 90 | 5 x 5 = 25 | 83 x 83 |
| Queen | 90 x 95 | 6 x 6 = 36 | 90 x 90 | 5 x 6 = 30 | 83 x 100 |
| King | 106 x 95 | 7 x 6 = 42 | 105 x 90 | 6 x 6 = 36 | 100 x 100 |
| California King | 102 x 99 | 7 x 7 = 49 | 105 x 105 | 6 x 6 = 36 | 100 x 100 |
Make a test block first
Sew one block and measure it before cutting fabric for 36. If it comes out 1/8 inch small, your seam allowance is slightly wide, and that error would add up to inches across a quilt. A scant 1/4 inch seam usually fixes it.
Tools for cutting and squaring 15 inch blocks
Olfa 60mm Ergonomic Squeeze-Handle Rotary Cutter RTY-3/DX
$26.49Cuts several layers of fabric at once, which speeds up cutting dozens of identical squares.
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Creative Grids 12-1/2 x 24-1/2 Rectangle Quilt Ruler
$55.99Long grippy ruler for cutting strips to the exact width before subcutting squares.
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Olfa 17 x 17 Rotating Cutting Mat RM-17S
$100.98A rotating mat lets you trim all four sides of a block without moving the fabric.
Check pricePrices change often, so confirm on Amazon. As an Amazon Associate we earn from qualifying purchases.
Frequently asked questions
What is the unfinished size of a 15 inch quilt block?
A 15 inch block is the finished size, measured after it is sewn into the quilt. Before that, it measures 15 1/2 x 15 1/2 inches, because each edge carries a 1/4 inch seam allowance that disappears into the seams. Trim blocks to exactly 15 1/2 inches with a square ruler before joining them so the rows line up.
How many 15 inch blocks do I need for a queen quilt?
A 90 x 95 inch queen quilt takes 6 blocks across and 6 down, 36 blocks in total, for a finished top of 90 x 90 inches. With 2 inch sashing between blocks you need 30 blocks. A border reduces the count further, so plan the layout before you piece every block.
What size squares do I cut for a 15 inch nine patch?
Each of the nine squares finishes at 5 inches, so cut them 5 1/2 x 5 1/2 inches. Sew three squares into each of three rows with 1/4 inch seams, press the seams in alternating directions so they nest, then join the rows. The block should measure 15 1/2 inches before it goes into the quilt.
What size half square triangles go in a 15 inch block?
In a four patch layout, each half square triangle finishes at 7 1/2 inches, cut from squares of 8 3/8 inches using the two-at-a-time method (or 8 1/2 inches if you prefer to trim). In a nine patch layout each HST finishes at 5 inches, cut from 5 7/8 inch squares.
How much fabric do I need for 15 inch nine patch blocks?
For a throw of 12 blocks, a two-color nine patch with five dark and four light squares per block needs 1 3/8 yards of dark and 1 1/8 yards of light fabric, cutting 5 1/2 inch squares from 42 inch strips. A queen of 36 blocks needs 4 and 3 1/4 yards.
Is 15 inches a good quilt block size?
15 inch blocks are big and fast: a queen quilt needs only 36, so large prints and simple designs shine. The trade-off is less room for intricate piecing to repeat across the quilt. Big blocks also mean long, heavy rows, where a machine with generous throat space makes joining and quilting more comfortable.
How we research: we compare manufacturer specifications, owner manuals, published standards and recurring themes in verified owner reviews. We do not test products in person, and this is researched guidance, not professional advice. Follow your machine manual and pattern, and take care with rotary cutters, hot irons and needles. As an Amazon Associate we earn from qualifying purchases.