Triangle Area Calculator
Calculate the area of a triangle from its base and height.
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How to use this tool
- Enter base and height in the fields above.
- Results update instantly as you type — or click Calculate.
- Read your area and the full breakdown beneath it.
Calculate triangle area using Area = (base × height) / 2.
Formula
Area = 1/2 × base × height
area = 0.5 * base * height
How it works
This calculator finds the area of a triangle given its base length and perpendicular height using the standard geometric formula: half the product of base and height. The height must be the perpendicular distance from the base to the opposite vertex, not a slant side length. The result is expressed in square units matching whatever unit the base and height are entered in.
Worked example
- Enter base = 6 and height = 4.
- Apply the formula: Area = 0.5 × 6 × 4.
- 0.5 × 6 = 3, then 3 × 4 = 12.
Area = 12 square units.
Common mistakes to avoid
- Forgetting the 1/2 factor and returning base × height instead of 0.5 × base × height.
- Using a slant side length as the height; the height must be perpendicular to the base, not a slanted edge.
- Applying this base-height formula to oblique triangles without first determining the true perpendicular height.
Key terms
- Base
- The bottom side of the triangle, chosen as the reference side for the area calculation.
- Perpendicular height
- The vertical distance from the base to the apex, measured at a right angle to the base — not the length of a slant side.
- Area
- The amount of two-dimensional space enclosed within the triangle, expressed in square units.
- Half-base rule
- Because a triangle is exactly half of a parallelogram with the same base and height, a factor of ½ always appears in the area formula.
Frequently asked questions
- How do you calculate the area of a triangle?
- Area = (base × height) / 2. The height must be perpendicular to the base.