Concrete quantity toolsCalculate the diagonal from the planned sides
For a planned rectangle, enter its two perpendicular side lengths in the diagonal calculator. It uses the Pythagorean theorem to calculate the expected distance between opposite corners. Keep both side lengths in the same unit; the result uses that unit too.
For example, a planned 12 ft by 16 ft rectangle has an expected diagonal of 20 ft. This is a comparison length derived from the planned dimensions, not a field measurement.
Measure between corresponding corners
Measure from the same defined point at each corner, then record both corner-to-corner diagonals if the project layout procedure calls for them. Compare each field measurement with the expected diagonal and compare the two field measurements with each other. Keep the endpoint labels and units with the readings so the measurements can be checked or repeated.
Understand what the diagonal check cannot confirm
A diagonal comparison can show a difference between the planned distance and a field measurement. It does not independently confirm the side lengths, corner angles, elevations, or complete layout. Even two equal diagonals do not establish all of those conditions.
Use the project's layout tolerances and checking procedure. This calculator and guide do not set an acceptable construction tolerance or approve a layout.