Triangle Area Calculator
Find a triangle’s area from its base and perpendicular height. The height must meet the chosen base at a right angle.
How to use Triangle Area Calculator
1. Choose Measurement Unit, then enter Base, Height without a unit suffix. 2. Use the selected ordinary, square or cubic unit for each measurement as explained below; changing the selector relabels inputs and does not convert them. 3. Select Calculate, or press Enter, and read triangle area. 4. Select Select Copy result to copy the answer, or Reset to clear the form.
Why use this tool?
Estimate the flat area of a triangular design without needing the lengths of all three sides.
How the calculation works
Triangle area = base × perpendicular height ÷ 2. The height may meet an extension of the base for an obtuse triangle. Results use up to six decimal places. Tiny nonzero results below 0.000001 use scientific notation with six significant digits. Browser floating-point arithmetic can introduce small rounding differences. Inputs and calculated magnitudes must not exceed 9,007,199,254,740,991. Negative physical measurements and arithmetic underflow are rejected. Zero dimensions are treated as a degenerate limit where the formula allows them; divisors and sides of an actual triangle must be positive. Formula reference: https://openstax.org/books/prealgebra-2e/pages/c-geometric-formulas
Example
Base = 10 cm and Height = 6 cm give 10 × 6 ÷ 2 = 30 cm².
Practical tip
Use perpendicular height, not a sloping side. A ruler measurement along the edge can overstate the area.
Frequently asked questions
Can the height fall outside the triangle?
Yes. In an obtuse triangle, the perpendicular height can meet the extended base outside the triangle; the same area formula applies.
Can I enter any two side lengths?
No. The second measurement must be perpendicular height relative to the selected base, rather than an arbitrary side.
Does changing Measurement Unit convert my numbers?
No. The selector states the unit of the numbers you enter and labels the answer. Convert measurements first when changing units. Area inputs use square units and volume inputs use cubic units; result precision follows the rounding method above.