Quilt Backing Calculator
The three layers shift while you quilt, so the backing is cut larger on every side. At 10 cm per side you need 170 × 220 cm, and 170 cm exceeds the usable width (107 − 2 = 105 cm), so two lengths have to be seamed: 220 × 2 = 440 cm to buy.
Your numbers
Backing needed
440cm
Pieces needed
2
Cut width
170cm
Formula
Backing needed = ⌈(Quilt width + 2 × Overhang per side) ÷ (Fabric width needed − 2)⌉ × (Quilt length + 2 × Overhang per side)
Trim the selvedges before seaming — they are woven tighter and pull that line into a ridge. Longarm quilters often ask for 10 cm or more per side, so check before cutting. Wide backing at 240 cm or more avoids the seam altogether.
What to enter
| Input | Default | Accepted range |
|---|---|---|
| Quilt width (cm)The finished quilt across, once bound. | 150 | 1 and up |
| Quilt length (cm)The finished quilt along, once bound. | 200 | 1 and up |
| Overhang per side (cm)Extra beyond each edge, absorbing shift while quilting. | 10 | 0 and up |
| Fabric width (cm)The fabric width; if it is sold folded, enter the opened width. | 107 | 10 and up |
Step by step
Quick reference table
Results when only Quilt width (cm) changes and everything else stays put.
| Quilt width (cm) | Backing needed (cm) | Pieces needed | Cut width (cm) |
|---|---|---|---|
| 75 | 220 | 1 | 95 |
| 113 | 440 | 2 | 133 |
| 150 | 440 | 2 | 170 |
| 225 | 660 | 3 | 245 |
| 300 | 880 | 4 | 320 |
What each result means
| Result | At default values |
|---|---|
| Backing needed (cm)Backing length to buy; too narrow a fabric must be pieced. | 440 |
| Pieces neededHow many pieces you need at that size. | 2 |
| Cut width (cm)The width to cut — finished size plus allowance. | 170 |
Common mistakes
Trim the selvedges before seaming — they are woven tighter and pull that line into a ridge. Longarm quilters often ask for 10 cm or more per side, so check before cutting. Wide backing at 240 cm or more avoids the seam altogether.
Glossary
- Quilt width
- The finished quilt across, once bound.
- Quilt length
- The finished quilt along, once bound.
- Overhang per side
- Extra beyond each edge, absorbing shift while quilting.
- Fabric width
- The fabric width; if it is sold folded, enter the opened width.
- Backing needed
- Backing length to buy; too narrow a fabric must be pieced.
- Pieces needed
- How many pieces you need at that size.
- Cut width
- The width to cut — finished size plus allowance.
Frequently asked questions
Q. How is Quilt Backing Calculator calculated?
Backing needed = ⌈(Quilt width + 2 × Overhang per side) ÷ (Fabric width needed − 2)⌉ × (Quilt length + 2 × Overhang per side) — The three layers shift while you quilt, so the backing is cut larger on every side. At 10 cm per side you need 170 × 220 cm, and 170 cm exceeds the usable width (107 − 2 = 105 cm), so two lengths have to be seamed: 220 × 2 = 440 cm to buy.
Q. Can you walk through an example?
With Quilt width 150cm, Quilt length 200cm, Overhang per side 10cm, Fabric width 107cm, the answer is Backing needed 440cm.
Q. What do I need to enter?
Enter Quilt width, Quilt length, Overhang per side, Fabric width. The result recalculates as you type, and an empty box counts as zero.
Q. How much does the answer move if I change a number?
Changing only Quilt width (cm) moves the answer to Quilt width (cm) 75 → Backing needed (cm) 220 and Quilt width (cm) 300 → Backing needed (cm) 880. The table below lays out five steps.
Q. How are the numbers rounded?
Money is shown to the nearest whole unit, percentages to one decimal place and everything else to two. What you see is rounded; the calculation itself carries the unrounded value forward.
Q. Anything to watch out for?
Trim the selvedges before seaming — they are woven tighter and pull that line into a ridge. Longarm quilters often ask for 10 cm or more per side, so check before cutting. Wide backing at 240 cm or more avoids the seam altogether.
Related calculators
Materials differ in density and absorption. If your label states a figure, use it — the defaults here are only common values.