Base and perpendicular height
Triangle Area Calculator
Enter the base and perpendicular height of a triangle. The height is measured at a right angle to the base.
Enter your measurements
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Use the base and perpendicular height
The formula is A = b × h ÷ 2. Choose one side as the base. Measure height at a right angle from that base, or its extended line, to the opposite vertex.
A sloping side is generally not the height. In an obtuse triangle, the perpendicular height may fall outside the triangle. The same formula still applies.
Example: base 8 m and height 5 m
8 × 5 ÷ 2 = 20 m², or approximately 215.28 ft².
Why divide by two?
A triangle takes up half the area of a parallelogram with the same base and height. This works for right, acute and obtuse triangles when the height is perpendicular to the chosen base.
For a right triangle, the two sides meeting at the right angle can be used as base and height. If you only know three side lengths, you must first determine the height or use a different method, such as Heron’s formula; this tool uses base and height.
Results are rounded for display. Calculations use unrounded values and international foot-based conversions. Enter actual lengths, rather than squared units.