Right-angle layout helper (Pythagorean theorem and diagonal check)
Calculate a theoretical diagonal from side lengths or a 3-4-5 setup, then compare measured differences with the tolerance.
The tool automatically suggests practical 3-4-5 marking lengths for field layout.
Enter conditions
Set the unit, reference method, tolerance, and measured values. The result panel updates instantly.
Review reference and judgement
Review the reference diagonal, recommended 3-4-5 markings, and each measurement’s OK/NG status on one screen.
How to use the checker
- Select the unit (mm/in) at the top.
- Choose either side-length input or 3-4-5 input, then enter values.
- Enter tolerance, optionally using quick chips.
- Enter measured diagonals and check difference + status for each row.
- Copy recommended 3k/4k/5k values or the judgement table when needed.
FAQ
What changes when I swap side A and side B?
Reference diagonal d stays the same, but the recommended 3-4-5 assignment—whether side A gets 3k or 4k—can change to make marking easier.
What if tolerance is empty?
Differences are still calculated, but the status is shown as “—”. Enter a tolerance to enable the OK/NG judgement.
What happens if pasted input contains text?
Only valid numeric values are imported; invalid tokens are skipped and reported.
Is a larger 3-4-5 setup better?
Generally, yes. Larger triangles are less sensitive to relative measurement error, so the tool recommends the largest practical scale.
Can I use fractions in inch mode?
Yes. Simple fractions such as 1/16 are accepted in quick chips and pasted input, then converted to decimals internally.
Notes
- This tool performs geometric calculation and difference judgement only. It does not verify code compliance or structural safety.
- Always measure from the same reference points (nail, mark, or corner). A shifted reference point adds error before calculation begins.
- Measure multiple times and review the spread. If it is large, check tension, alignment, and hook contact first.