Quick answer: how to calculate fabric for one fabric
Cut width equals finished width plus 2 times seam allowance, and cut length equals finished length plus 2 times seam allowance. Pieces per strip equal fabric width divided by cut width, rounded down. Strips needed equal pieces needed divided by pieces per strip, rounded up. Total fabric length equals strips times cut length. Yardage to buy is total length divided by 36, rounded up to the nearest 1/8 yard.
Example: a finished rectangle 4 by 6 inches, seam 0.25 inch, 80 pieces needed, fabric width 44 inches. Cut size is 4.5 by 6.5 inches, pieces per strip are 9, strips needed are 9, total length is 58.5 inches, exact yardage is 1.63 yards, yardage to buy is 1.63 yards.
Scope, stated plainly: this calculator handles one fabric and one piece size at a time. It does not calculate a whole quilt in one run. For a whole quilt, calculate each fabric separately, with its own piece size and count, and never add yardages of different fabrics into one buy. For borders, backing, batting, and binding, use their own calculators, because each has its own seam and rounding rules.
If you only need a number, use the Fabric Calculator. If you want to understand why pieces per strip rounds down and strips round up, read on.
What fabric calculation means, for one fabric
Fabric calculation, for one fabric, means working out how much yardage you need to cut a certain number of pieces, of a certain finished size, from fabric of a certain width. It is not a guess from quilt size alone, because the same quilt top can use many fabrics, in different piece sizes and different counts.
That is why this guide, and the Fabric Calculator, work one fabric at a time. Repeat the calculation for each fabric in your quilt top, with that fabric's piece size and piece count, and buy each fabric separately. Do not add yardages of different fabrics together into one buy, because you cannot cut one fabric's pieces from another fabric.
Finished size compared with cut size
| Finished size | Cut size, with 0.25 inch seam allowance |
|---|---|
| 5 by 5 inches | 5.5 by 5.5 inches |
| 4 by 6 inches | 4.5 by 6.5 inches |
| 3 by 3 inches | 3.5 by 3.5 inches |
| 2.5 by 4.5 inches | 3 by 5 inches |
Finished size is the size a piece will be after it is sewn into the quilt top. Cut size is finished size plus seam allowance on both sides. For quilt piecing, seam allowance is usually 0.25 inch, so cut size is finished size plus 0.5 inch in each direction, because 0.25 inch is added on each side.
Step by step: how to calculate fabric
Step 1: Get cut piece size
Cut piece width equals finished piece width plus 2 times seam allowance. Cut piece length equals finished piece length plus 2 times seam allowance. Seam allowance is added on both sides, so it is counted twice.
Step 2: Work out pieces per strip
Pieces per strip equals fabric width divided by cut piece width, rounded down to the next whole piece. Only whole pieces count, because a partial piece cannot be used. Pieces are cut in strips across fabric width, with strip width equal to cut piece length, and pieces laid side by side across the strip.
Step 3: Work out strips needed
Strips needed equals number of pieces needed divided by pieces per strip, rounded up to the next whole strip. The last strip is only partly used, but you must buy the whole strip, because fabric is bought by length, not by piece.
Step 4: Work out total fabric length
Total fabric length equals strips needed times cut piece length. Total length is the length of fabric you need to cut, from the roll or from yardage, before rounding to yardage to buy.
Step 5: Work out yardage
Exact yardage equals total fabric length divided by 36 in inch mode. Yardage to buy is exact yardage rounded up to the nearest 1/8 yard. In centimetre mode, metres to buy are rounded up to the nearest 0.1 metre.
Try it with the calculator: Use the Fabric Calculator with your own finished piece size, piece count, fabric width and seam allowance. It uses the same steps as this guide, and it shows cut size, pieces per strip, strips needed, total length and yardage together.
Worked example: rectangles, not squares
Take a finished rectangle 4 by 6 inches, seam allowance 0.25 inch, pieces needed 80, fabric width 44 inches.
Cut piece size: width 4 plus 2 times 0.25 equals 4.5 inches. Length 6 plus 2 times 0.25 equals 6.5 inches.
Pieces per strip: 44 divided by 4.5 equals 9.77, rounded down, equals 9 pieces. The leftover width, 44 minus 9 times 4.5, which is 3.5 inches, is not enough for another piece, so it is waste, not a tenth piece.
Strips needed: 80 divided by 9 equals 8.88, rounded up, equals 9 strips. The last strip gives 9 pieces, but only 8 are needed from it, because 8 strips give 72 pieces, and 80 minus 72 equals 8.
Total fabric length: 9 times 6.5 equals 58.5 inches.
Exact yardage: 58.5 divided by 36 equals 1.63 yards. Yardage to buy, rounded up to the nearest 1/8 yard, equals 1.63 yards, because 1.625 rounds to 1.63 at two decimal places.
Check by area, for sense: 80 pieces, each cut 4.5 by 6.5 inches, total cut area is 2340 square inches. Fabric bought, 58.5 inches long and 44 inches wide, total area is 2574 square inches. The difference is strip waste, from rounding pieces per strip down and strips needed up, which is normal, not a mistake.
Pieces per strip table, our own computed table
This table is computed from the same rule as the calculator, pieces per strip equal fabric width divided by cut width, rounded down, at fabric width 44 inches. It is not copied from another site. Leftover width is not a piece, it is waste.
| Cut width | Pieces per strip, at 44 in fabric | Leftover width |
|---|---|---|
| 2.5 in | 17 | 1.5 in |
| 4.5 in | 9 | 3.5 in |
| 5 in | 8 | 4.0 in |
| 6.5 in | 6 | 5.0 in |
| 10 in | 4 | 4.0 in |
How to make sure your result is correct
- Cut size check. Cut width and cut length must each equal finished size plus 2 times seam allowance, not plus 1 times seam allowance.
- Pieces per strip check. Pieces per strip must be rounded down. Rounding up would promise a piece that does not fit in the strip width.
- Strips check. Strips must be rounded up. Strips times pieces per strip must be at least pieces needed, never below it.
- Total length check. Total length must equal strips times cut length, not pieces times cut length, because pieces share strips.
- Buy versus exact check. Buy yardage must never be below exact yardage. If it is, you rounded the wrong way.
- One fabric check. Each fabric must be calculated separately. Adding yardages of different fabrics into one buy gives a number that buys neither fabric correctly.
How to count pieces, without missing any
- Count pieces by fabric, not by quilt block alone. A block that uses the same fabric in two places counts twice for that fabric, once for each place.
- Count pieces for the whole quilt top, including borders if the same fabric is used there, and including any extra pieces for testing or for mistakes, if you want a safety margin. Safety margin is your own choice, not part of the calculation, so add it to piece count before calculating, if you want it.
- Check piece count against your pattern, block by block, before buying. A pattern that says 12 blocks, each with 4 pieces of fabric A, means 48 pieces of fabric A, not 12.
- If a fabric is used in two different piece sizes, calculate each size separately, and buy each size's yardage separately, even if it is the same fabric. You cannot cut a larger piece from the yardage calculated for a smaller piece, unless the larger piece also fits in the strips from that calculation.
Common mistakes with fabric calculation
- Using finished size as cut size. Finished size does not include seam allowance. Cut size is finished size plus seam allowance on both sides. Using finished size as cut size gives pieces that are too small after sewing.
- Rounding pieces per strip up. Pieces per strip must be rounded down, because only whole pieces count. Rounding up pretends a partial piece is a whole piece, and you will come up short.
- Rounding strips needed down. Strips needed must be rounded up, because you must buy the whole last strip, even if it is only partly used.
- Adding yardages of different fabrics together. Yardage for fabric A cannot be used to cut fabric B. Buy each fabric separately, with its own calculation.
- Forgetting directional prints. If a fabric has a directional print, and pieces must all run the same way, you cannot rotate pieces to fit more per strip. This calculator assumes pieces can be laid as described, with width across fabric width. If your print is directional, check layout before buying.
Calculate your own fabric yardage now
Use your finished piece size, piece count, fabric width and seam allowance in the calculator, and check the result against the steps in this guide.
Open the Fabric CalculatorFrequently asked questions
Add seam allowance to both sides of finished piece size to get cut piece size. Work out how many cut pieces fit across fabric width, then how many strips you need for your total piece count, then total fabric length, and convert total length to yardage, rounded up to the nearest eighth yard.
Finished size is the size a piece will be after it is sewn into the quilt top. Cut size is finished size plus seam allowance on both sides. For a 5 inch finished square with 0.25 inch seam allowance, cut size is 5.5 inches, because 0.25 inch is added on each side.
Count pieces by fabric, not by block alone. A block that uses the same fabric in two places counts twice for that fabric. Multiply blocks by pieces per block, for each fabric, and check against your pattern before buying.
Yes, but one fabric at a time. Repeat the calculation for each fabric in your quilt top, with that fabric's piece size and piece count, and buy each fabric separately.
Yes, because pieces per strip depends on fabric width. A wider fabric fits more pieces per strip, so fewer strips are needed, and total length is lower. That is why fabric width must be entered as usable width, not just nominal width, if your fabric is narrower after prewashing or trimming selvedges.
Related guides and calculators
Next, read How to Calculate Pieces to Yardage for yardage from cut pieces, and How to Calculate Piece Count for pieces from yardage you already own. For one fabric from finished size, use the Fabric Calculator.