Triangle Area Calculator
Find a triangle's area from base and height, three sides, or two sides and the angle between.
What the Triangle Area Calculator does
Three ways into the same answer. Base times height halved is the classic. Heron's formula works from three sides alone with no angle needed. The SAS form uses the sine of the angle between two known sides.
Formula
Area = ½ × base × heightHeron: s = (a+b+c) ÷ 2, Area = √(s(s−a)(s−b)(s−c))SAS: Area = ½ × a × b × sin(C)
Inputs explained
| Input | Unit | Required | Notes |
|---|---|---|---|
| Known values | one of 3 options | Yes | — |
| Base | number | In some modes | Accepts more than 0. Shown Known values is Base and height. |
| Height | number | In some modes | Accepts more than 0. Shown Known values is Base and height. |
| Side a | number | In some modes | Accepts more than 0. Shown Known values is Three sides (Heron's formula), or Known values is Two sides and included angle. |
| Side b | number | In some modes | Accepts more than 0. Shown Known values is Three sides (Heron's formula), or Known values is Two sides and included angle. |
| Side c | number | In some modes | Accepts 0 or more. Shown Known values is Three sides (Heron's formula). |
| Included angle | ° | In some modes | Accepts more than 0, up to 180. Shown Known values is Two sides and included angle. |
How to use it
- Choose Known values.
- Fill in the remaining inputs the form shows for your choice.
- Select Calculate.
Worked example
A triangular plot with sides 13 m, 14 m and 15 m.
- Method
- Three sides
- a
- 13
- b
- 14
- c
- 15
s = 21, Area = √(21×8×7×6) = √7056 = 84 m².
Frequently asked questions
What is the height in the base × height formula?
The perpendicular distance from the base to the opposite vertex, not the length of a slanted side.