Area and Geometry Calculator
Find the area and perimeter (or circumference) of common shapes for flooring, painting, gardening or homework, in the unit of your choice.
Result
Enter your values and select Calculate to see the result.
How to use this calculator
- Choose a shape and the unit your measurements are in.
- Only the fields needed for that shape are shown.
- For triangles, use base and perpendicular height for area only, or three sides to get both area and perimeter.
- For circles, enter either the radius or the diameter.
Formula
- Rectangle:
area = length × width,perimeter = 2 × (length + width) - Square:
area = side²,perimeter = 4 × side - Triangle (base and height):
area = ½ × base × height - Triangle (three sides, Heron’s formula):
s = (a + b + c) ÷ 2,area = √(s(s − a)(s − b)(s − c)) - Circle:
area = π × r²,circumference = 2 × π × r
Worked example
A room 8 m by 5 m
Area: 8 × 5 = 40 m². Perimeter: 2 × (8 + 5) = 26 m.
Triangle with sides 7, 8 and 9 cm
s = 12, so area = √(12 × 5 × 4 × 3) = √720 ≈ 26.83 cm². Perimeter: 24 cm.
Circle with radius 3 m
Area: π × 3² ≈ 28.27 m². Circumference: 2 × π × 3 ≈ 18.85 m.
Assumptions and limitations
- All measurements must use the same unit; area is given in that unit squared.
- Three sides must satisfy the triangle inequality (each side shorter than the other two combined).
- When ordering materials such as flooring or paint, add an allowance for waste and overlaps.
Frequently asked questions
Why can’t I get a perimeter from base and height?
Many different triangles share the same base and height but have different side lengths. Enter all three sides to calculate the perimeter.
How do I convert square meters to square feet?
Multiply by about 10.7639, because one meter is 3.28084 feet and area scales with the square of length.