Quilt Size Calculator

Quilt sizing and fabric yardage calculations ensure you purchase the right amount of fabric before cutting, which avoids the nightmare of running short mid-project on a fabric that has since been discontinued.

Basic quilt area: Quilt Area (sq in) = Width × Length

Fabric yardage for a solid backing: Backing Yardage = (Quilt Length + 8 in seam/stretch allowance) × Number of Fabric Widths Needed / 36 Where fabric width is typically 44" or 60" (selvage to selvage).

Block-based patchwork formula: Blocks Needed = Ceiling(Width / Block Size) × Ceiling(Length / Block Size) Fabric per color = (Blocks for that color × Piece Area) × Waste Factor (1.1–1.15)

Two sets of numbers, and people mix them up constantly

The dropdown asks for a mattress size. The table below lists finished quilt sizes. They are different measurements and the gap between them is the drop, which is what you enter as the side drop above.

A twin mattress is 39" × 75". Add a 12" drop down each side and 12" at the foot and you land on 63" × 87", which is roughly the 66" × 90" that shops call a twin quilt. So the two agree, as long as you know which one you are reading.

Standard finished quilt sizes:

Worked example, a throw quilt (50" × 65") in 5" finished blocks:

• Blocks across: ⌈50/5⌉ = 10, blocks down: ⌈65/5⌉ = 13, so 130 blocks
• Two fabrics alternating: 65 blocks of each
• Cut size per block: 5" + two ¼" seams = 5½", not the 5" of the finished block. Forgetting the seam allowance is the classic way to come up short
• Seven 5½" squares fit across 42" of usable width, so 65 blocks take ⌈65/7⌉ = 10 rows
• Fabric per colour: 10 × 5½" = 55", plus 12% waste = 61.6" = 1¾ yards

Note that this counts rows rather than dividing by area. Area says 1½ yards, and area is wrong, because the 3½" left at the end of each row is too narrow for another square.

Batting allowance: Add 3–4 inches to each dimension for the batting (for quilting take-up). Backing needs 4–6 inches total extra on all sides.