Area Calculator
Pick a shape, enter its measurements in meters or feet, and get the area in square meters, square feet, square yards and acres — plus the perimeter wherever the measurements determine it.
Formula and calculation
Worked example
A rectangle 5 m long and 3 m wide covers 15 square meters — which is 161.4587 square feet — and its perimeter is 16 meters.
Why some shapes here have no perimeter
Area and perimeter are not equally sensitive to your inputs. A triangle given a base and a height has a fixed area, but its other two sides can swing around freely — so there are infinitely many perimeters with that same area, and printing one would be a guess. The same is true of a trapezoid given its two bases and height, and a parallelogram given a base and a height: the slanted sides are not pinned down, and the perimeter changes as the shape leans. Fill in the three sides of a triangle, or use a rectangle or a circle, and the calculator reports the perimeter alongside the area.
Heron's formula, and when to use base × height
The two triangle entries give identical results — they are the same number by different routes. Use base × height when you can measure a perpendicular height, which is typical for rooms, roofs and land plots you can sight across. Use the three sides when the height is awkward or impossible to reach: a triangular garden bed or a parcel of land with a stream across it. Heron's formula needs all three sides to be valid, though — any two must add up to more than the third — and 3, 4, 5 works out to 6 exactly, because it is a right triangle with the base and height hiding in plain sight.
What the results mean
- Area
- The surface the shape covers, in square meters — the flat region inside its edges. One square meter is about 10.76 square feet.
- Area in square feet
- The same area in square feet, the unit US flooring, roofing and paint estimates are usually quoted in.
- Area in square yards
- The same area in square yards — how carpet and landscaping materials are often ordered. One square yard is 0.836 square meters.
- Area in acres
- The same area in acres (1 acre = 4,046.86 m² = 43,560 ft²), the unit land is measured in. A typical suburban lot is a small fraction of an acre.
- Perimeter
- The distance around the outside of the shape, in meters. It is shown only when your inputs determine the sides, so some shapes here report no perimeter rather than guess one.
- Calculation
- The area formula for the shape you picked, with your numbers substituted in, so the arithmetic can be checked line by line.
Frequently asked questions
How do I find the area of a triangle without the height?
Use Heron's formula with the three side lengths: s is half the perimeter, and the area is the square root of s(s − a)(s − b)(s − c). For sides 3, 4 and 5, s is 6 and √(6 × 3 × 2 × 1) = 6 — the same answer as base × height ÷ 2.
How do I convert square meters to square feet?
Multiply by 10.7639, because 1 meter is 3.28084 feet and the factor is squared (3.28084² = 10.7639). So 15 m² is 161.46 ft². Dividing by the same number converts back from square feet to square meters.
What is the difference between area and perimeter?
Area is the surface inside the shape, measured in square units; perimeter is the distance around the edge, measured in plain units. A 5 m by 3 m rectangle has an area of 15 m² and a perimeter of 16 m — and shapes with the same perimeter can have very different areas.
How big is an acre?
One acre is 43,560 square feet, or 4,046.86 square meters — about 0.405 of a hectare, and roughly the size of a standard American football field without the end zones. In the other direction, a single square meter is 0.000247 acres.