Triangle Area
Calculate the area of a triangle from its base and height using the formula area = base x height / 2.
- Base x Height
- 60 units squared
This uses the base-height method. Make sure the height is measured perpendicular to the chosen base. Both values must use the same unit; the area is returned in that unit squared.
What the Triangle Area Calculator Does
This tool finds the area of a triangle when you know its base and the height that goes with that base. Enter two numbers and it returns the area in square units, so you don't have to multiply and divide by hand.
It's handy for students checking geometry homework, DIY and construction work (figuring out paint, flooring, or material for a triangular section), drafting, sewing, and anyone who needs a quick, reliable triangle area.
How It Works: The Triangle Area Formula
The calculator uses the standard base-times-height formula:
area = (base x height) / 2
The key detail is that the height must be the perpendicular height: the straight-line distance from the base to the opposite corner (vertex), measured at a 90-degree angle to the base. It is not the length of a slanted side. Any side of the triangle can act as the base, as long as you pair it with the matching perpendicular height to the opposite vertex.
Worked Example with Real Numbers
Suppose a triangle has a base of 8 cm and a perpendicular height of 5 cm. Plug the values into the formula:
- Multiply base by height: 8 x 5 = 40
- Divide by 2: 40 / 2 = 20
- Area = 20 square centimeters (cm2)
Why Divide by 2
A triangle is exactly half of a rectangle (or parallelogram) that shares the same base and height. The rectangle's area is base x height, so the triangle covers half of it.
This is why the same formula works for every triangle, whether it is right-angled, acute, or obtuse, as long as you use the perpendicular height for the base you chose.
Tips and Common Mistakes
Most errors come from using the wrong height or mixing units. Keep these points in mind:
- Use the perpendicular height, not a sloping side. For an obtuse triangle the height can fall outside the triangle, and that is fine.
- Match the base to its own height. The base and the perpendicular distance must correspond to the same triangle, not two different sides.
- Keep units consistent. Convert everything to the same unit (e.g., all centimeters) before calculating.
- Area units are squared. A result from centimeters is in cm2, from meters in m2, and so on.
- If you only know the three side lengths and no height, this base-and-height method won't apply directly; you would need Heron's formula instead.
Frequently asked questions
How do I find the area of a triangle?
Multiply the base by the height and divide by 2. The height must be the perpendicular distance from the base to the opposite vertex.
Does it matter which side I use as the base?
No. You can use any side as the base, as long as the height is measured perpendicular to that chosen base. The area will be the same.
What units does the result use?
If base and height are in the same unit (for example centimeters), the area is in that unit squared (square centimeters).
What if I only know the three side lengths?
This calculator uses base and height. If you only have the three sides, you would need Heron's formula instead, which is a different method.