How to use the precut quilt calculator
- Pick a preset for your kind of precut (jelly roll, charm pack, layer cake, honey bun or mini charm), or type your own piece width, length and pieces per pack.
- Enter the number of packs and the size to cut each patch, with the seam allowances included.
- Read the whole patches you get per piece and in all, the finished size of a patch and the fabric left over per piece.
- Use the layout table to see near-square quilt tops that use most of the patches, with their finished size before borders.
Formula
patches per piece = round down(piece width / cut width) x round down(piece length / cut length), or the same with the patch turned a quarter turn, whichever is larger
total patches = patches per piece x pieces per pack x packs
finished patch = cut size - 2 x seam allowance on each side
finished top = columns x finished width by rows x finished length
Whole patches only: a part of a patch is wasted, never counted.
One jelly roll
A jelly roll has 40 strips 2.5 inches wide and 42 inches long. Cutting patches 2.5 by 4.5 inches gives round down(42 / 4.5) = 9 patches per strip, so 360 patches in all, with 3.75 square inches left over per strip. With a seam allowance of 0.25 inch each patch finishes at 2 by 4 inches. A grid of 24 columns by 15 rows uses all 360 patches and finishes at 48 by 60 inches.
Two charm packs of 42 five-inch squares used as they are give 84 patches. One layer cake of 42 ten-inch squares cut into 5-inch patches gives 4 per square and 168 in all.
Counting pieces, not area
Dividing the area of the fabric by the area of a patch overstates what you can cut, because pieces come in whole sizes and every strip has a short end that cannot be used. Counting how many whole patches fit along the length of a strip and across its width gives a result you can trust. The calculation also tries the patch turned a quarter turn, which sometimes yields more.
Real packs vary by maker, and pinked edges lose a little width, so measure your own pack and trim the numbers. The presets are example pack sizes, not standards.
From patches to a quilt
The layout table shows grids that use at least 80 percent of your patches and are close to square after you apply the finished size. Borders, sashing and the backing come next: the quilt sashing and border calculator and the quilt backing and binding calculator cover them. To go between finished and cut block sizes, use the quilt block size calculator, and for any fabric, the fabric yardage calculator.
Assumptions and limits
- Pieces are straight rectangles with the width and length you enter, and every piece in the pack is the same size.
- The seam allowance is the same on all sides and the cut size includes it.
- Presets are example pack sizes. Washing, pressing and trimming change the real size.
- Layouts use whole patches in a rectangular grid, with no borders.
Frequently asked questions
Why is the patch count different from my area estimate?
Area estimates ignore the waste at the ends of strips and the unused part of each square. Counting whole patches is more accurate for cutting.
What does left over mean?
It is the area of fabric in one piece that is not part of a whole patch. It is useful for scrap, binding or small blocks.
Can I use half-square triangles?
This page counts square and rectangular patches only. Triangle patches are cut from squares, so you can count the squares here and then divide as your pattern says.
Why does the layout table skip some shapes?
It lists the squarest grids that use most of your patches. A very long thin grid might use every patch but would not make a usable quilt, so it is left out.