Rectangle Area Calculator
Calculate the area, perimeter and diagonal of a rectangle from its length and width in any unit.
Your inputs
Results
Area
15 m²
- Perimeter
- 16 m
- Diagonal
- 5.830952 m
✓Exact calculation — rounded only for display
What this calculator does
The most common area calculation — rooms, plots, screens and sheets of material.
Formula and method
Area = length × width; Perimeter = 2(length + width); Diagonal = √(length² + width²)
Worked example
Calculated by this tool with its default inputs:
Inputs
- Length unit: Metres
- Length: 5
- Width: 3
Results
- Area: 15 m²
- Perimeter: 16 m
- Diagonal: 5.830952 m
How to read the results
Use the area converter to switch between square metres and square feet.
Assumptions and limitations
- Use one length unit consistently; areas are in square units and volumes in cubic units of that length.
Quantities and costs are planning estimates. Add sensible allowances, and check with suppliers, carriers or professionals before buying, shipping or building.
Questions
How do I measure an L-shaped room?
Split it into rectangles, calculate each, then add the areas.
Methodology and verification
- Result type
- Exact mathematical calculation (rounded only for display)
- Formula version
- 1.0
- Automated verification
- 2 reference and validation test cases, checked against independently computed values. The site cannot be built if any of them fail.
- Editorial review
- Awaiting human editorial review. The explanation was drafted with AI assistance; the formula and examples are verified by the automated tests above.
Privacy
Everything you enter is calculated in this browser and is not sent to Numerith or anyone else. Inputs are added to a share link only if you choose to include them. Privacy policy