SHAPES, DATA, AND SCHOOL MATH
Area and Perimeter Calculator
Calculate the area and perimeter of a square, rectangle, triangle, or circle with shape-specific inputs and visible formulas.
Review your result
Your result
Ready when you are.
Enter your values and select Calculate. Your result stays on this device.
How it works
Rectangle area = length × width; square area = side²; triangle area = base × height ÷ 2; circle area = π × radius².
Assumptions
Dimensions use the same linear unit. A triangle perimeter requires all three side lengths, so this tool reports triangle area only.
About this calculator
This free area calculator answers a broad U.S. search need without hiding which geometry formula is active. Choose a shape first, then enter only the measurements that apply to it.
How to use it
- Choose square, rectangle, triangle, or circle.
- Enter dimensions in one consistent unit.
- Calculate and compare the area with the available perimeter or circumference result.
- For floors, lots, or material orders, verify measurements and use the project-specific square footage tool.
Use case
area calculator: a clear planning check
Choose a square, rectangle, triangle, or circle, enter consistent dimensions, and calculate area with the active formula kept visible.
Calculate area for a common shape and review its perimeter or circumference when the entered dimensions support it.
Source and update
Last reviewed: 2026-08-22
NIST Guide for the Use of the International System of UnitsFrequently asked questions
How do I calculate the area of a rectangle?
Multiply length by width when both measurements use the same unit.
Can this calculate area and perimeter together?
Yes for squares, rectangles, and circles. A triangle perimeter needs three sides, while this form asks for base and perpendicular height.
Does the answer have to be in square feet?
The interface labels feet for U.S. use. The same formulas work with any single consistent unit, and the area is expressed in that unit squared.
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