Geometry

Triangle Area & Perimeter

Area uses the base and the perpendicular height — the straight-line distance from the base to the opposite corner. Perimeter uses the three side lengths, and the tool checks that those sides can actually form a triangle.

InputsA = ½bh

What do you want to find?Base (area only)Perpendicular height (area only)Side a (perimeter only)Side b (perimeter only)Side c (perimeter only)Unit

Step-by-step

waiting

Fill in the fields and press Solve. The full method will appear here, one numbered step at a time.

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Worked example

Find the area of a triangle with base 10 cm and perpendicular height 6 cm.

1.
A triangle fills exactly half of the rectangle drawn around its base and height.
```
A = ½ × b × h
```
2.
Substitute the base and the perpendicular height.
```
A = ½ × 10 × 6
```
3.
Multiply the base by the height, then halve it.
```
= 60 ÷ 2 = 30 cm²
```

Answer: Area = 30 cm²

Note: Area needs the perpendicular height. Side lengths that can’t form a triangle are rejected.

Use “Load worked example” above to run this in the solver.

Related formulas

The formulas this tool uses, each explained with symbols, conditions and its own example in the Formula Library.

Area of a triangleA = ½ × b × h Perimeter of a triangle and the triangle inequalityP = a + b + c, where a + b > c, a + c > b, b + c > a