Seam Allowance Calculator
Add a separate allowance to each edge of a finished rectangle to get the cut size.
Calculator
Calculated in your browser. These measurements are not sent to the server.
Result
- Cut width
- 11 in (27.94 cm)
- Cut height
- 13 in (33.02 cm)
Each edge uses the allowance you enter. Preset buttons only fill the fields; they do not override a number you change afterward.
No general seam allowance is treated as the correct amount for every project.
Cut plan
EdgeLeft
Allowance0.5 in (1.27 cm)
EdgeRight
Allowance0.5 in (1.27 cm)
EdgeTop
Allowance0.5 in (1.27 cm)
EdgeBottom
Allowance0.5 in (1.27 cm)
| Edge | Allowance |
|---|---|
| Left | 0.5 in (1.27 cm) |
| Right | 0.5 in (1.27 cm) |
| Top | 0.5 in (1.27 cm) |
| Bottom | 0.5 in (1.27 cm) |
How this calculation works
Cut width is finished width plus the left allowance plus the right allowance.
Cut height is finished height plus the top allowance plus the bottom allowance.
Preset buttons fill the four edges with a common value. The result uses whatever numbers remain after you edit them.
Worked example
10 by 12 in piece with uneven side allowances
Left 1 in and right 1/4 in make a cut width of 11.25 in.
Top and bottom allowances of 1/2 in each make a cut height of 13 in.
Assumptions and limitations
- Allowances are added, not included in the finished size already.
- No allowance amount is treated as the correct general seam allowance.
- Curves, clipping, and hem fold-backs that are not a simple added edge are not modeled.
Common questions
Which seam allowance is correct?
It depends on the pattern and the fabric. Use the preset as a starting fill, then change any edge that your project treats differently.
Can one edge be zero?
Yes. Zero is allowed. A negative allowance is rejected and is not turned into a positive number.