How to use frame squareness diagonal check
What this calculation does
A diagonal check compares two corner-to-corner measurements and gives the ideal diagonal for a rectangle with the entered target dimensions.
Enter target width and height, then measure both diagonals between corresponding opposite corners.
Enter the measurements
- Target rectangle width: Enter the target rectangle width.
- Target rectangle height: Enter its target height.
- Measured diagonal A: Measure diagonal from one corner pair.
- Measured diagonal B: Measure the other corner-to-corner diagonal.
Formula and variables
Ideal diagonal = sqrt(width² + height²). Diagonal difference = absolute value of measured diagonal A − measured diagonal B.
Ideal diagonal = square root of width squared plus height squared. Measured difference is the absolute difference between the two readings.
Read the result
A 48×36 in target has a 60 in ideal diagonal; readings of 59.8 and 60.2 in differ by 0.4 in.
Worked example
Inputs: 48 × 36 in target; measured diagonals 59.8 and 60.2 in
- Ideal = √(48²+36²) = √3600 = 60 in.
- Difference = |59.8−60.2| = 0.4 in.
Expected result: 60 in ideal diagonal; measured diagonals differ by 0.4 in
Frequently asked questions
Do equal diagonals prove a frame is flat?
No. This is a squareness check, not a complete size or flatness tolerance.
What difference is acceptable?
The project tolerance is not prescribed by this calculator.
Conditions, presets and technical notes
Assumes a rectangular target with diagonals measured between corresponding opposite corners. Equal diagonals are a squareness check, not a complete dimensional or flatness tolerance; the user decides acceptable deviation.