Triangle Area Calculator
½bh or Heron from sides a, b, c. Click any i for detail.
Triangle
Mode
i
Mode
Base×height or Heron (three sides). |
|
|---|---|
Base
i
Base
Base length. |
|
Height
i
Height
Perpendicular height to that base. |
|
Side a
i
a
First side length. |
|
Side b
i
b
Second side length. |
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Side c
i
c
Third side length. |
How to use this calculator
- Choose base×height or Heron mode.
- Enter the matching fields.
- Read the area.
- Invalid Heron sides return 0.
Results explained
Area = ½ × base × height when height is known. Heron’s formula uses semi-perimeter s = (a+b+c)/2 and area = √[s(s−a)(s−b)(s−c)] when all three sides are known.
Quick reference: triangle area
½bh or √[s(s−a)(s−b)(s−c)].
| Item | Detail |
|---|---|
| Base 10, height 5 | Area 25 |
| 3-4-5 triangle | Area 6 |
| Triangle inequality | Required for Heron |
| Obtuse triangles | Height may fall outside |
Keep all lengths in the same unit.
How the estimate is built
area = 0.5×base×height; Heron: s=(a+b+c)/2, area=√[s(s−a)(s−b)(s−c)].
Example scenario
Base 10, height 5 → 25; 3-4-5 → 6.
FAQ
Height not perpendicular?
Use the altitude to the chosen base.
Ambiguous SSA?
Heron needs three sides, not an angle.
Equilateral shortcut?
Area = √3/4 × side² — or use Heron.
See circle?
For circular area πr².