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Half-Square Quilt Cutting Size Calculator
Find a starting square size for the seven-eighths-inch quilting method.
- Formula & worked example
- Private in your browser
- No signup
Calculator inputs
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How to use this calculator
- Enter the known values in the units shown. Results update as you type.
- Edit a calculated value to solve backwards, or lock a value to hold it fixed.
- Use the worked example to check the method. Reset restores the starting fields.
Private by default
Inputs and results stay in this browser tab. Bookify does not upload or store the values you enter.
Formula and method
For the traditional two-at-a-time half-square triangle method, add 7/8 inch to the finished square size. A finished size of 10 centimeters starts from a 12.2225-centimeter square. Its diagonal is the starting side length multiplied by the square root of two.
Starting side = finished side + 7/8 inch; diagonal = starting side × √2
Worked example
Enter these known values and leave the other values blank.
- Finished length and width
- 10 cm
- Length and width of raw square
- 12.223 cm
- Diagonal
- 17.285 cm
Assumptions and limitations
- The formula uses the traditional 7/8-inch allowance. It does not add a separate oversizing allowance. Follow your pattern if it calls for larger squares or a different construction method.
- Use the units shown beside each field. This model assumes the stated relationship and does not account for quantities left out of the formula.
Common questions
Does this include extra room for trimming?
The formula uses the traditional 7/8-inch allowance. It does not add a separate oversizing allowance. Follow your pattern if it calls for larger squares or a different construction method.
References
The calculation equations, inverse formulas, units, and input rules were imported from this source. Bookify provides the interface and equation solver.
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