Quick answer: how to calculate precut pieces
Start from cut size, not finished size, because seam allowance is already in the cut size, and the calculator adds no seam allowance. Pieces per precut, as entered, equal floor of precut width divided by cut width, times floor of precut length divided by cut length. Pieces per precut, rotated, equal the same calculation with cut width and length swapped. Pieces per precut chosen equal the larger of the two. Total pieces equal pieces per precut times number of precuts. Partial pieces are always rounded down, never up.
Example: 3 fat eighths, each 9 by 22 inches, cut piece 4 by 6 inches. As entered gives 2 across times 3 along, which is 6 pieces. Rotated gives 1 across times 5 along, which is 5 pieces. Chosen is 6 pieces per precut, total is 18 pieces.
Usable size warning, stated plainly: the calculator uses precut sizes exactly as entered, with no deduction for squaring, selvage, or shrinkage. A nominal fat quarter is 18 by 22 inches, but after squaring it can be smaller. If you trimmed your precut, enter the trimmed size, not the nominal size, or the count will be too high. Competitors use different usable sizes, 17.5 by 20.5 inches, 17 by 20 inches, and others, which is why their yields differ, and why our guide states its size up front instead of hiding it.
If you only need a number, use the Fat Quarter and Precut Calculator. If you want to understand why rotation matters, and what each precut yields, read on.
What a fat quarter and a precut mean
A precut is fabric already cut to a standard size, sold in bundles, so you do not have to cut yardage first. A fat quarter is the most common precut, and it is 18 by 22 inches. A fat eighth is 9 by 22 inches. A charm square is 5 by 5 inches. A layer cake square is 10 by 10 inches. A jelly roll strip is 2.5 by 44 inches. A mini charm square is 2.5 by 2.5 inches.
A fat quarter is one quarter yard of 44 inch fabric by area, 396 square inches, cut in half across the width, so it is wider and shorter than a regular quarter yard cut, which is 9 by 44 inches. Both are one quarter yard by area, but the fat quarter is more useful for larger pieces, because it is wider.
Common precut sizes, compared
| Precut type | Size | Area |
|---|---|---|
| Fat quarter | 18 by 22 inches | 396 square inches |
| Fat eighth | 9 by 22 inches | 198 square inches |
| Charm square | 5 by 5 inches | 25 square inches |
| Layer cake square | 10 by 10 inches | 100 square inches |
| Jelly roll strip | 2.5 by 44 inches | 110 square inches |
| Mini charm square | 2.5 by 2.5 inches | 6.25 square inches |
Precut area alone does not tell you piece count, because piece count depends on piece size and orientation, and on leftover width and leftover length. A precut with a large area can still give few pieces, if the cut piece does not fit well in its width or length.
Step by step: how to calculate fat quarter and precut pieces
Step 1: Choose precut size
Choose precut size from the precut type you own, for example fat eighth 9 by 22 inches, or enter a custom precut size if your precut is not a standard size. Precut size is used as entered, with no seam allowance added, because cut size already includes seam allowance.
Step 2: Work out pieces per precut, as entered
Pieces per precut, as entered, equals pieces across precut width times pieces along precut length, both rounded down to whole numbers, because a partial piece cannot be cut. Pieces across precut width equals precut width divided by cut piece width, rounded down. Pieces along precut length equals precut length divided by cut piece length, rounded down. For fat eighth 9 by 22 inches and cut piece 4 by 6 inches, pieces across width equals 9 divided by 4, equals 2.25, rounded down to 2 pieces, pieces along length equals 22 divided by 6, equals 3.66, rounded down to 3 pieces, and pieces per precut, as entered, equals 2 times 3, equals 6 pieces.
Step 3: Work out pieces per precut, rotated
Pieces per precut, rotated, swaps cut piece width and length, and repeats the same calculation. Pieces across precut width, rotated, equals precut width divided by cut piece length, rounded down. Pieces along precut length, rotated, equals precut length divided by cut piece width, rounded down. For fat eighth 9 by 22 inches and cut piece 4 by 6 inches, pieces across width, rotated, equals 9 divided by 6, equals 1.5, rounded down to 1 piece, pieces along length, rotated, equals 22 divided by 4, equals 5.5, rounded down to 5 pieces, and pieces per precut, rotated, equals 1 times 5, equals 5 pieces.
Step 4: Work out chosen pieces per precut and total pieces
Chosen pieces per precut equals the larger of as entered and rotated. For as entered 6 pieces and rotated 5 pieces, chosen pieces per precut equals 6 pieces, as entered orientation. Total pieces you can cut equals chosen pieces per precut times number of precuts you own. For chosen pieces per precut 6 pieces and number of precuts 3, total pieces you can cut equals 6 times 3, equals 18 pieces.
Try it with the calculator: Use the Fat Quarter and Precut Calculator with your own precut type, number of precuts and cut piece size. It uses the same steps as this guide, and it shows precut size used, pieces per precut in both orientations, chosen pieces per precut, total pieces and chosen orientation, together.
Worked example: 3 fat eighths, cut 4 by 6 inch pieces
Take precut type fat eighth, 9 by 22 inches, number of precuts 3, cut piece 4 by 6 inches.
Pieces per precut, as entered: pieces across width 9 divided by 4, equals 2.25, rounded down to 2 pieces, pieces along length 22 divided by 6, equals 3.66, rounded down to 3 pieces, total 2 times 3, equals 6 pieces.
Pieces per precut, rotated: pieces across width 9 divided by 6, equals 1.5, rounded down to 1 piece, pieces along length 22 divided by 4, equals 5.5, rounded down to 5 pieces, total 1 times 5, equals 5 pieces.
Pieces per precut, chosen: 6 pieces, as entered orientation, because 6 is larger than 5.
Total pieces you can cut: 6 times 3, equals 18 pieces.
In this example, rotation gives fewer pieces, not more, because the narrow precut width 9 inches fits only one 6 inch piece across, while the as entered layout fits two 4 inch pieces across. Rotation is not always better, it depends on precut size and cut piece size, so both orientations must be checked.
Pieces per fat quarter table, our own computed table
This table uses a fat quarter of 18 by 22 inches, exactly as entered in the calculator, and square cut pieces, so as entered and rotated give the same count. It is computed from the same floor rule as the calculator, not copied from another site. For rectangular pieces, always test both orientations, because the larger count wins, and the fat eighth example above shows rotation can also give fewer pieces.
| Square cut size | Pieces across 18 in | Pieces along 22 in | Pieces per fat quarter |
|---|---|---|---|
| 2.5 in | 7 | 8 | 56 |
| 5 in | 3 | 4 | 12 |
| 10 in | 1 | 2 | 2 |
Precut presets in the calculator, for reference: fat quarter 18 by 22 inches, fat eighth 9 by 22 inches, charm square 5 by 5 inches, layer cake square 10 by 10 inches, jelly roll strip 2.5 by 44 inches, mini charm square 2.5 by 2.5 inches, plus a custom size you enter. A honey bun is not a preset in this calculator, use custom size for it.
How to make sure your result is correct
- Cut versus finished check. Inputs must be cut size, with seam allowance already included, not finished size, or every piece will be too small.
- Both orientations check. As entered and rotated must both be computed, and the larger count chosen, unless the print is directional and must not be rotated.
- Round down check. Across and along counts must both be rounded down. Rounding either up would promise a piece that does not fit.
- Total check. Total pieces must equal pieces per precut times number of precuts, never area divided by piece area.
- Usable size check. Enter trimmed usable size, not nominal size, if the precut was squared or shrunk, or the count will be too high.
- Top only check. This count is for pieces from precuts only. Backing, binding, borders, and sashing are extra, and are not included in this count.
When precut piece count is enough, and when it is not
- Precut piece count is enough when: you need rectangular cut pieces in the stated layout, with no directional print constraint, and you will check piece count before cutting.
- Precut piece count is not enough when: your precut has a directional print and pieces must all run one way, your pieces must be cut in a specific orientation, or your pieces are not rectangles. In those cases, check piece layout before cutting, and use the as entered orientation, not the rotated orientation, if rotation would turn the print the wrong way.
- Precut piece count does not fix a wrong cut size: if you use finished size instead of cut size, piece count will be too high, because finished size is smaller than cut size. Use cut size, which already includes seam allowance, in the calculator.
Common mistakes with fat quarters and precuts
- Using finished size as cut size. Finished size is smaller than cut size, because cut size already includes seam allowance. For example, a finished 3.5 inch piece, with 0.25 inch seam on each side, is cut 4 inches. Use cut size, not finished size, in the calculator.
- Assuming rotation is always better. Rotation can give more pieces, fewer pieces, or the same count, depending on precut size and cut piece size. Always check both orientations, and choose the larger count, unless a directional print forbids rotation.
- Rounding piece count up. Piece count must be rounded down at pieces across width and at pieces along length, because a partial piece cannot be cut. Rounding up would count pieces you cannot actually cut.
- Counting precuts for the whole quilt at once. Count precuts by fabric, not by quilt, if different fabrics use different precut types. Adding precut counts for different fabrics into one count gives the wrong count for each fabric.
Calculate your own precut piece count now
Use your precut type, cut piece size and precut count in the calculator, and check the result against the steps in this guide.
Open the Fat Quarter and Precut CalculatorFrequently asked questions
It depends on cut piece size and orientation. A fat eighth is 9 by 22 inches. For 4 by 6 inch cut pieces, a fat eighth gives 2 pieces across 9 inches and 3 pieces along 22 inches, which is 6 pieces per fat eighth, as entered orientation. Three fat eighths give 18 pieces.
A fat quarter is 18 by 22 inches, which is one quarter yard of 44 inch fabric, cut in half across the width, so it is wider and shorter than a regular quarter yard cut, which is 9 by 44 inches.
Both are one quarter yard of fabric by area, 396 square inches. A fat quarter is 18 by 22 inches. A regular quarter yard cut is 9 by 44 inches. The fat quarter is more useful for larger pieces, because it is wider.
Rotate cut pieces only if rotation gives more pieces and if your fabric has no directional print constraint. Rotation can give more pieces, fewer pieces, or the same count, depending on precut size and cut piece size. Always check both orientations, and choose the larger count, unless a directional print forbids rotation.
No. Precut piece count assumes rectangular pieces, cut in the stated layout. For triangles, circles, or other shapes, check piece layout before cutting, and do not rely on precut piece count alone.
Related guides and calculators
Next, read How to Calculate Piece Count for pieces from yardage, and How to Calculate Quilt Fabric for yardage from finished size. For precuts themselves, use the Fat Quarter and Precut Calculator.