29/07/2026
How to Square a Corner Using the 3-4-5 Rule
The 3-4-5 rule is a simple and reliable method used in construction to create a perfect 90° corner. It is based on the Pythagorean theorem (3² + 4² = 5²) and is widely used for building layouts, foundations, walls, and formwork.
Steps
1. Mark the starting point where the two sides will meet.
2. Measure 3 m along the first side and place a stake.
3. Measure 4 m along the second side and place another stake.
4. Measure the diagonal distance between the two marks.
5. Adjust the layout until the diagonal measures exactly 5 m.
6. Once the diagonal is correct, the corner is a perfect 90° angle.
Advantages
Ensures accurate right-angle layouts.
Prevents alignment errors in foundations and walls.
Quick, simple, and cost-effective.
Suitable for residential and commercial construction.
Common Mistakes
Measuring from incorrect reference points.
Using stretched or damaged measuring tapes.
Not securing stakes firmly.
Ignoring uneven ground conditions.
Failing to recheck all measurements before excavation.
