Math
Triangle Area Calculator
Use the triangle area calculator when you know a triangle's base and perpendicular height.
Try an example
Result
Area
—
- Matching rectangle area
- —
Student quick launch
Grade planning, algebra checks, and formulas students reach for most.
Study path
Use this calculator with
Follow these when you want the formula behind the answer, a short lesson, or nearby tools in the same topic.
What the triangle area calculator solves
Use the triangle area calculator when you know a triangle's base and perpendicular height.
Formula
How to use it
- Enter a base length.
- Enter the perpendicular height to that base.
- Use square units for the area.
How to read the answer
A triangle is half of a rectangle or parallelogram with the same The number being raised to a power, or the side a shape's height is measured from. and height.
Common mistakes and edge cases
- Height must be perpendicular to the base.
- Slanted side length is not always height.
- Use matching length units.
Worked examples
Whole-number triangle
Area
42
Decimal dimensions
Area
8.8
Frequently asked questions
What if I know three sides instead?+
Use Heron's formula or a triangle calculator. This page uses base and perpendicular height.
Can the height be outside the triangle?+
Yes for obtuse triangles; the perpendicular height can fall outside the visible triangle.
About this calculator
- Written by
- mathcheck editorial team
- Last reviewed
- May 15, 2026
Method
- Uses the values entered by the user and stable formulas documented on the page.
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Last updated: May 15, 2026