Area of a Triangle Calculator

Three formulas: base × height ÷ 2, SAS (two sides and angle), and Heron's (three sides).

Inputs

Result

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How to use this calculator

  • Pick a method.
  • Fill in the values for that method (the third field changes meaning per mode).
  • Read the area.

About this calculator

Three classic formulas for triangle area, picked by which inputs you have. Base × height when you have a perpendicular height. SAS (½ a b sin C) when you have two sides and the angle between. Heron's formula when you have all three sides — works for any triangle as long as the three sides satisfy the triangle inequality.

Frequently asked

When should I use Heron's formula?+
When you know the three side lengths but not any angles. It's the most general formula.
What is the SAS formula good for?+
When you have two sides and the included angle (the angle between them). Common in surveying and trigonometry problems.
Does base × height require a right angle?+
No — height is the perpendicular distance from the base to the opposite vertex, regardless of the triangle being right-angled.
What if my three sides don't form a valid triangle?+
Heron's formula returns "—" when the triangle inequality (any side < sum of other two) is violated.
Can I find a side from the area?+
For ½ × base × height, yes: side = 2A / height. For Heron, no — there are infinitely many triangles with a given area.

Related calculators

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A = ½ × (parallel side a + parallel side b) × height.
Area of a Parallelogram Calculator
A = base × height (perpendicular height).
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a² + b² = c². Solve for hypotenuse or missing leg of a right triangle.
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P = a + b + c. Sum of all three sides.
Distance Between Two Points (2D + 3D)
d = √(Δx² + Δy² [+ Δz²]). Pythagorean distance in the plane or 3-space.
Area of a Rhombus Calculator
A = (d₁ × d₂) / 2 — half the product of the diagonals.

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