Compute the area of a triangle from its base and height, or from all three side lengths with Heron’s formula.
Choose how the area is computed — base × height or side lengths (Heron).
Length of the triangle base — any side can serve as the base. Must be positive when mode uses base/height.
Perpendicular height from base to opposite vertex — the altitude, not a slant side.
Used in Heron mode.
Used in Heron mode.
Used in Heron mode.
Area
12.0000
Measure of the surface enclosed by the triangle, in square units of your inputs.
Perimeter
—
Total length around the triangle when sides are known.
Method
A = b·h ÷ 2
Which formula was applied given the mode.
What this means
Half the area of the enclosing rectangle (or Heron when only sides are known). The base×height form is exact when the altitude is correct.
The area of a triangle can be found from its base and height, or — when you only know the three sides — from Heron’s formula.
Formula
A = b·h ÷ 2 | A = √(s(s − a)(s − b)(s − c)), s = (a + b + c) ÷ 2
Worked examples
FAQ
What if my three side lengths don’t form a triangle?
The sum of any two sides must exceed the third. If not, the shape cannot exist and the tool reports an error.
Which method is more accurate?
Both are exact to the displayed precision. Use base × height when you know the height; otherwise use the three sides.