Triangle Area Calculator
Find the area of any triangle from what you can measure. Use base and height if you have them, three sides if you do not (Heron’s formula), or two sides and the angle between them.
- Perimeter
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Formula
How to use it
- Choose which measurements you know.
- Enter them with their units; angles can be in degrees or radians.
- Read the area. With three sides, or two sides and an angle, you also get the perimeter.
Worked examples
Base 10 ft and height 6 ft: 30 ft², which is 2.787 m²
- Area
- 30 ft²
Sides of 3 m, 4 m and 5 m (Heron’s formula)
- Area
- 6 m²
- Perimeter
- 12 m
Sides of 7 m and 10 m with 30° between them
- Area
- 17.5 m²
- Perimeter
- 22.27 m
When you cannot measure the height
The height must be perpendicular to the base, which is awkward to measure on a plot of land or a piece of fabric. Measuring the three edges and using Heron’s formula avoids the problem entirely.
Equilateral shortcut
For a triangle with three equal sides, area = (√3 ÷ 4) × side², or about 0.433 × side². A 6-inch equilateral triangle is 15.59 square inches.
Questions people ask
What is the area of a triangle with base 10 and height 6?
½ × 10 × 6 = 30 square units.
What is the area of a 3-4-5 triangle?
6 square units. It is a right triangle, so the two short sides are the base and height: ½ × 3 × 4.
Why is the result blank for my three sides?
The sides cannot form a triangle. Each side must be shorter than the sum of the other two.