Triangle Area Calculator
There are three standard ways to find a triangle’s area depending on what you know. Choose the method that matches your measurements — base and height, all three sides, or two sides with the angle between them — and get the area instantly.
Results
Formula
How to use this calculator
- Choose the method that matches the measurements you have.
- Fill in just the fields that method needs.
- Press Calculate — the area (and perimeter, when the sides are known) appears.
Worked example
Base 12, height 5.
- Multiply base by height: 12 × 5 = 60.
- Halve it: 60 ÷ 2 = 30.
Result: The area is 30 square units.
Frequently asked questions
Why is triangle area exactly half of base × height?
Any triangle is half of the parallelogram built on the same base and height — duplicate the triangle, rotate it 180°, and the pair forms that parallelogram.
When does Heron’s formula fail?
When the three lengths cannot form a triangle (the two shorter ones must exceed the longest). The calculator checks this and explains the error.
Which angle does the two-sides method need?
The included angle — the one between the two sides you enter. Other angles need the law of sines first.
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