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Quilt Block Size Calculator: Finished and Cut Block Size for Any Quilt Layout

Last updated Researched from specs, manuals and owner reviews We earn from qualifying purchases
Quick answer

Subtract the borders and all sashing from the quilt width, then divide by the blocks across. A 50 x 65 inch throw with 5 blocks across needs 10 inch finished blocks, cut 10 1/2 inches. A 90 inch queen with 6 blocks, 2 inch sashing and 5 inch borders needs 11 5/8 inch blocks.

Know the quilt size you want and how many blocks you want to see? This calculator works out the block size, rounds it to a cuttable 1/8 inch, flags sizes that land on easy ruler lines, and tells you how far the top comes out from your target. The reverse box does the opposite: start with a block size and get the layout.

Your quilt layout

Finished, between blocks

Finished, each side

Uses the quilt size, sashing and border above

Your results

Finished block size

10 in

Trim blocks to 10 1/2 x 10 1/2 in unfinished

Exact math10 in
Rounded down to 1/8 in10 in
Ruler friendlyYes, on a 1/4 in line
Grids that divide evenly2 x 2, 4 x 4, 5 x 5
Actual top size50 x 60 in
Short of target0 in wide, 5 in long

Reverse: blocks needed at 12 in

4 x 5 = 20 blocks

Top 48 x 60 in

Machines that handle this quilt comfortably

Baby, crib and wall quilts fit through almost any machine. A good computerized machine with a walking foot and wide table is plenty.

Prices change often, so confirm on Amazon. As an Amazon Associate we earn from qualifying purchases.

How do you calculate quilt block size?

Block size is what is left of the quilt after the borders and sashing take their share, divided evenly among the blocks. Work in finished sizes, the measurements that show after sewing, and add the seam allowance only at the end.

  1. Subtract the borders. Borders sit on both sides. A 90 inch wide queen with 5 inch borders leaves 80 inches for the center.
  2. Subtract the sashing between blocks. Six blocks across have five gaps. At 2 inches each that is 10 inches, leaving 70 inches.
  3. Divide by the blocks across. 70 / 6 = 11.667 inches. Repeat for the length: (95 minus 10 minus 10) / 6 = 12.5 inches.
  4. Use the smaller answer so the blocks stay square. Here the width limits it to 11.667 inches.
  5. Round down to the nearest 1/8 inch, since rulers are marked in eighths: 11 5/8 inches finished. Add 1/2 inch for seam allowance: trim blocks to 12 1/8 inches.

With 11 5/8 inch blocks, the top measures 89 3/4 x 89 3/4 inches, 1/4 inches narrower and 5 1/4 inches shorter than planned. That gap is normal. Widen the top and bottom borders, add another row of blocks, or accept a slightly smaller quilt. A 1/4 inch here and there disappears once the quilt is washed and draped over a bed.

What size blocks fit each standard quilt size?

The table starts from 12 inch blocks, finds the nearest whole number of blocks across and down, then asks the calculator for the exact block size that fills each quilt. Sizes follow the coverlet convention in our quilt size chart, with no sashing or borders.

Block size that fills each quilt, starting near 12 in
QuiltTarget (in)LayoutExact blockRounded to 1/8Top size (in)
Baby 40 x 40 3 x 3 13.33 13 1/4 in 39 3/4 x 39 3/4
Crib 36 x 52 3 x 4 12 12 in 36 x 48
Lap 45 x 60 4 x 5 11.25 11 1/4 in 45 x 56 1/4
Throw 50 x 65 4 x 5 12.5 12 1/2 in 50 x 62 1/2
Twin 68 x 90 6 x 8 11.25 11 1/4 in 67 1/2 x 90
Twin XL 68 x 95 6 x 8 11.33 11 1/4 in 67 1/2 x 90
Full / Double 83 x 90 7 x 8 11.25 11 1/4 in 78 3/4 x 90
Queen 90 x 95 8 x 8 11.25 11 1/4 in 90 x 90
King 106 x 95 9 x 8 11.78 11 3/4 in 105 3/4 x 94
California King 102 x 99 9 x 8 11.33 11 1/4 in 101 1/4 x 90

Notice that a square block can only match one dimension exactly. Most bed quilts are longer than they are wide, so the block size is set by the width and the length is adjusted with borders or an extra row.

How many blocks of each size does a queen quilt need?

Working the other way, here is the layout for common block sizes on a 90 x 95 inch queen with no sashing or borders, rounding to the nearest whole block. Each block size links to its own page with cut sizes and grid breakdowns.

Queen quilt layouts by finished block size
BlockUnfinishedAcross x downTotal blocksTop size (in)
6 inch 6 1/2 in 15 x 16 240 90 x 96
8 inch 8 1/2 in 11 x 12 132 88 x 96
9 inch 9 1/2 in 10 x 11 110 90 x 99
10 inch 10 1/2 in 9 x 10 90 90 x 100
12 inch 12 1/2 in 8 x 8 64 96 x 96
14 inch 14 1/2 in 6 x 7 42 84 x 98
16 inch 16 1/2 in 6 x 6 36 96 x 96

Measure a test block before cutting the rest

Sew one block and measure it. If it comes out 1/8 inch small, your seam is a little wide. Fix the seam now, because an 1/8 inch per seam across 6 blocks can cost you most of an inch.

What does "ruler friendly" mean for a block size?

The flag asks a practical question: can you cut this without squinting? Every rotary ruler has 1/8 inch marks, but 1/4 and 1/2 inch lines are bolder and easier to read, especially in lower light or with progressive lenses. A finished block of 10 inches lands on a quarter inch line. A block of 11 5/8 inches needs an eighth inch line, which is still cuttable but slower and less forgiving.

The grid line matters just as much. A block design is drawn on a grid: a four patch is 2 by 2, a nine patch 3 by 3, and a sawtooth star 4 by 4. If the finished block divided by the grid does not land on an eighth, the pieces inside the block cannot be cut accurately either. That is why the calculator lists which grids divide your block evenly. If the one you need is missing, adjust the block size by an eighth or a quarter and let the borders absorb the change.

Should you change the quilt size or the block size?

Change whichever is cheaper to change. Blocks are the expensive part: every size change ripples into the cut size of every piece. Borders are the cheap part. The usual order of adjustment is:

  • First, pick a clean block size near the calculator's answer, ideally a whole inch that fits your block design's grid.
  • Second, change the count of blocks across or down to get close to the target.
  • Third, set the sashing. Sashing stretches a layout by the strip width times the number of gaps.
  • Last, size the borders to make up the remaining inches, using different widths on the sides and ends if the quilt must hit an exact length.

When the layout is set, plan fabric with the quilt fabric yardage calculator and the strips with the sashing and border calculator. Bigger blocks also mean a bigger quilt to push through the machine, so check the throat space calculator before you commit to a king.

Safety note: Rotary cutters are extremely sharp: close the blade guard whenever you set one down and cut away from your body.

Frequently asked questions

How do I figure out what size quilt blocks to make?

Start with the finished quilt width, subtract both borders and every sashing strip between blocks, and divide what is left by the number of blocks across. Do the same for the length and use the smaller answer so the blocks stay square. A 90 x 95 inch queen with 6 by 6 blocks, 2 inch sashing and 5 inch borders works out to 11.667 inches, which rounds down to 11 5/8.

What is the difference between finished and unfinished block size?

Finished size is what shows in the quilt after the blocks are sewn together. Unfinished size includes a 1/4 inch seam allowance on every edge, so it is 1/2 inch larger. A 10 inch finished block is trimmed to 10 1/2 inches before you sew it to its neighbors. Patterns list both, and this calculator shows both.

Why round quilt block size down to the nearest 1/8 inch?

Rotary rulers are marked in 1/8 inch steps, so a block of 11.667 inches cannot be cut accurately. Rounding down to the nearest 1/8 keeps every cut on a ruler line and makes the top a little smaller than planned, never bigger. Make up the difference with a slightly wider border, which is much easier to adjust than dozens of blocks.

What block sizes are easiest to piece?

Whole inch sizes that divide evenly by the grid of the block design are easiest. A 12 inch block splits cleanly into 2, 3, 4 and 6 unit grids, which is why so many patterns use it. A 10 inch block splits into 2, 4 and 5 unit grids but gives awkward thirds. The calculator lists which grids land on 1/8 inch ruler lines for your block.

How many 12 inch blocks do I need for a throw quilt?

A 50 x 65 inch throw with no sashing or borders takes 4 blocks across and 5 down, 20 blocks in all, for a 48 x 60 inch top. That is close enough to adjust with borders. Use the reverse box in the calculator to try any block size, sashing and border combination.

Should sashing be included in the block size?

No. Sashing is separate from the block, so subtract it first. Count the strips between blocks, which is one fewer than the blocks across when there is no outer sashing frame. Five blocks across with 2 inch sashing uses 4 strips, or 8 inches of the width. The sashing and border calculator handles framed sashing with cornerstones.

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.