Precut conversion calculator
Three conversions, all honest about direction. Pieces to precuts: how many packs a cutting list takes. Yardage to precuts: what a yard on your shelf cuts into. And the swap: the pattern calls for one precut, your stash holds another, and the calculator says in plain words whether it covers the call and what the shortfall is.
Cutting from a 5 in reference: a squared fat quarter yields 12 charm squares, and a yard of 44 in fabric yields 56.
Precut reference
| Precut | Cut size | Usable size used here | Standard pack |
|---|---|---|---|
| Charm square (5 x 5 in) | 5 x 5 in | 5 x 5 in | 42 pieces |
| Mini charm (2.5 x 2.5 in) | 2.5 x 2.5 in | 2.5 x 2.5 in | 42 pieces |
| Layer cake (10 x 10 in) | 10 x 10 in | 10 x 10 in | 42 pieces |
| Jelly roll strip (2.5 in x width of fabric) | 2.5 x 42 in | 2.5 x 42 in | 40 pieces |
| Fat quarter (18 x 22 in) | 18 x 22 in | 17.5 x 21.5 in | sold singly |
| Fat eighth (9 x 22 in) | 9 x 22 in | 8.5 x 21.5 in | sold singly |
Rolls of 40 strips, 2.5 in by width of fabric.
The formula, in words
Pieces are packed into the usable area of the precut on a grid, rotating pieces when the print allows and refusing to rotate when you mark it directional. Counts per precut times the pieces per pack gives the pack yield; packs needed rounds up, because shops do not sell fractions of a pack. Yardage equivalents are area based and labeled as estimates: they tell you what a precut buy is worth in yardage, not what a shop will charge. A fat quarter cut from a yard uses the standard four fat quarters per yard of 44 in fabric.
Worked example
One fat quarter, squared to 17.5 x 21.5 in of usable fabric, yields 12 charm squares at 5 in: three across and four down. One yard of 44 in fabric yields 56 charm squares. Those two figures anchor the whole table below, and the calculator reproduces them exactly.
Questions quilters ask
Why is the pieces-per-pack number editable?
Because brands do not agree. One maker's charm pack holds 42 squares, another's holds 40 or 44, and jelly rolls run 40 strips at most brands but not all. The defaults are the common standards; set the number on the pack you are actually buying.
Can I swap a layer cake for charm packs?
Yes, one 10 in layer cake square cuts into four 5 in charms, so the swap runs in your favor on count. The swap tool does this arithmetic for every pair of precuts and says the result in pieces, including the shortfall when the swap runs the wrong way.
What does directional print change?
A directional print cannot be rotated to fit, so pieces pack in one orientation only and the yield can drop. Marking a project directional here gives the honest, lower count instead of the optimistic one.
Are fat eighths worth it?
An eighth of a yard cut as a fat eighth, 9 x 22 in, is far more usable than a skinny 4.5 in strip off the bolt at the same area. For small pieces and applique, fat eighths give real cutting room. The reference table shows the usable size the calculator packs against.