Enter the base and height of a triangle to find its area.
Base times height, halved
The area of a triangle is half its base times its height. The key detail is that the height must be measured perpendicular to the base, straight up from it to the opposite corner, not along a slanted edge. Any of the three sides can act as the base as long as you pair it with the matching perpendicular height.
When you do not know the height but do know all three side lengths, a different approach called Heron formula gives the area directly. For the common classroom and everyday case, though, base and height is the fastest route.
The formula
Worked example
A triangle with base 10 and height 6 has area 0.5 x 10 x 6 = 30.
How to read your result
The height must be measured perpendicular to the base, not along a slanted side. Any side can serve as the base as long as you use the matching perpendicular height.
Frequently asked questions
- What counts as the height?
- The perpendicular distance from the base to the opposite vertex.
- What if I only know the three sides?
- Use Heron formula instead, which works from the side lengths.
- What units does the area use?
- The square of whatever unit you enter for base and height.
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