FORMULAS, SHAPES, TIME, AND NUMBER TOOLS
Area Calculator
Calculate the area of a rectangle, square, triangle, or circle with shape-specific measurements and visible formulas.
Review your result
Your result
Ready when you are.
Enter your values and choose Calculate. Your inputs stay on this device.
How it works
Rectangle = length × width; square = side²; triangle = base × height ÷ 2; circle = πr².
Assumptions and limits
All measurements use one consistent linear unit. Triangle perimeter needs all three sides and is not inferred from base and height.
About this calculator
This shape-first area calculator asks only for the dimensions required by the selected formula.
What this tool helps you check
Calculate shape area with the selected formula and consistent units visible beside the result.
How to use it
- Review the formula and assumptions shown for this area calculator.
- Choose a shape and enter every length in the same unit.
- Calculate and review area and the available boundary measurement.
- Verify real site measurements, survey boundaries, and construction allowances separately.
Source and update
Last reviewed: 2026-08-22
NIST — Guide for the Use of the International System of UnitsFrequently asked questions
What does this area calculator calculate?
This shape-first area calculator asks only for the dimensions required by the selected formula.
How should I interpret the result?
Review area and the available boundary measurement. The result changes whenever an input or assumption changes.
Is the result official or guaranteed?
Verify real site measurements, survey boundaries, and construction allowances separately.
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