Quilt Block Calculator
Planning a quilt requires knowing how many blocks you need, how large the finished top will be, and how much fabric to buy for sashing and borders. The finished quilt width equals the block size multiplied by the number of columns, plus sashing strips between and on each side of the columns, plus the border on both sides. The same logic applies to the height using the number of rows. Sashing fabric requirements depend on the total sashing area divided by your fabric width (typically 44 inches for quilting cotton), with a 10 percent waste allowance added for squaring up and seam allowances. Border yardage is estimated from the quilt perimeter multiplied by border width, with 15 percent extra. This calculator uses finished (sewn) dimensions throughout: enter your block size after sewing and pressing, not the cut size. A standard 12-inch finished block is cut at 12.5 inches to include a quarter-inch seam allowance on each side. The results give you a solid starting point for purchasing fabric; always round up to the nearest quarter yard when buying.
Finished quilt: -- in wide x -- in tall
Quilt size formula
All dimensions use finished (sewn) measurements in inches.
quilt_width = (block_size x blocks_wide) + (sashing x (blocks_wide + 1)) + (border x 2) quilt_height = (block_size x blocks_tall) + (sashing x (blocks_tall + 1)) + (border x 2) total_blocks = blocks_wide x blocks_tall
Yardage estimation
block_area = total_blocks x block_size x block_size (sq in) quilt_area = quilt_width x quilt_height (sq in) sashing_area = quilt_area - block_area (sq in) sashing_yd = (sashing_area / (fabric_width x 36)) x 1.10 border_perim = 2 x (quilt_width + quilt_height) (in) border_yd = (border_perim x border_width / (fabric_width x 36)) x 1.15
Round up to the nearest quarter yard when purchasing. For pieced sashing with cornerstones, calculate each fabric separately.
Common quilt size reference
| Quilt type | Typical finished size | Common block layout |
|---|---|---|
| Crib / baby | 36 x 54 in | 3 x 4 blocks at 12 in |
| Lap / throw | 54 x 72 in | 4 x 6 blocks at 12 in |
| Twin | 60 x 80 in | 5 x 6 blocks at 12 in |
| Full / Double | 80 x 96 in | 6 x 8 blocks at 12 in |
| Queen | 90 x 108 in | 7 x 8 blocks at 12 in |
| King | 108 x 108 in | 8 x 8 blocks at 12 in |
Quilt block calculator: frequently asked questions
How do I calculate the finished size of a quilt?
Multiply the block size by the number of blocks in each direction, then add the sashing and border. For example, twelve 12-inch blocks arranged 4 wide by 3 tall with 2-inch sashing and a 3-inch border gives: width = (12 x 4) + (2 x 5) + (3 x 2) = 48 + 10 + 6 = 64 inches. This calculator does the arithmetic for you once you enter your values.
What is sashing in quilting?
Sashing is the fabric strips sewn between quilt blocks to separate and frame them. Sashing appears both vertically (between columns of blocks) and horizontally (between rows). Setting the sashing width to zero removes it from the layout. Sashing adds visual space and can make a smaller number of blocks fill a larger quilt top.
How much fabric do I need for sashing?
The calculator estimates sashing yardage by subtracting the total block area from the quilt top area, dividing by the fabric width (44 inches by default), and adding a 10 percent waste allowance for squaring up and seam allowances. This is an approximation; cutting layouts vary, and pieced sashing with cornerstones requires a different calculation.
How much border fabric do I need?
Border yardage is estimated from the perimeter of the quilt top multiplied by the border width, divided by fabric width, plus a 15 percent allowance. Mitered border corners require more fabric than straight-cut corners. For very wide borders or striped fabrics, add extra yardage and verify your cutting layout before purchasing.
What seam allowance is assumed?
This calculator works with finished (sewn) dimensions, not cut dimensions. Enter the finished block size (after sewing and pressing). If your blocks are cut at 12.5 inches with a quarter-inch seam allowance on all sides, the finished size is 12 inches. Enter 12 in the block size field.
Sources and methodology
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. Yardage estimates include waste allowances; always round up and buy extra for first-time projects. See our methodology.