Triangle Area Calculator

Calculate triangle area

Enter base and perpendicular height. The result shows the half-rectangle relationship.

What is the Area of a Triangle?

A triangle is a three-sided polygon with three vertices and three edges. The area of a triangle is the total space enclosed within its three sides, measured in square units such as square meters (m²), square feet (ft²), or square centimeters (cm²).

The most common method to calculate a triangle's area uses the base (any side of the triangle) and the height (the perpendicular distance from the base to the opposite vertex). This formula works for all types of triangles: equilateral, isosceles, scalene, and right triangles.

How Triangle Area Is Calculated

Follow these detailed steps:

  1. Step 1: Identify Base and Height
    Base is any side. Height is the perpendicular distance from base to opposite vertex. They must be perpendicular.
  2. Step 2: Apply the Formula
    Area = ½ × base × height. For base 10 feet and height 6 feet: A = ½ × 10 × 6 = 30 square feet.
  3. Step 3: Verify Units
    Ensure base and height are in the same units. The result will be in square units.

Triangle Area Formula

Area = (Base × Height) / 2

Or written mathematically:

A = (b × h) / 2 or A = ½ × b × h

Where:

  • A = Area of the triangle
  • b = Base of the triangle
  • h = Height (perpendicular to the base)

Examples

Basic Triangle Example

Problem: Calculate the area of a triangle with base 10 cm and height 6 cm.

Solution:

  1. Base = 10 cm
  2. Height = 6 cm
  3. Area = (10 × 6) / 2 = 60 / 2 = 30 cm²

Right Triangle Example

Problem: A right triangle has legs of 8 inches and 15 inches. What is its area?

Solution: In a right triangle, the two legs can serve as base and height.

  1. Base = 8 inches, Height = 15 inches
  2. Area = (8 × 15) / 2 = 120 / 2 = 60 in²

Quick Calculation Tips

  • Height must be perpendicular to base - not along a slanted side
  • Any side can be the base, but you need the matching height
  • Right triangles: the legs serve as base and height
  • For Heron's formula (knowing 3 sides): s = (a+b+c)/2, A = √(s(s-a)(s-b)(s-c))

Common Mistakes to Avoid

  • Using slanted side as height
    Height must be perpendicular (90°) to the base. A slanted side is not the height.
  • Forgetting the ½
    Area is half of base × height, not the full product. 10 × 6 = 60, but area is 30.

Frequently Asked Questions

Why is the triangle area divided by 2?

A triangle is essentially half of a rectangle or parallelogram with the same base and height. Imagine drawing a diagonal through a rectangle - you get two identical triangles, each with half the rectangle's area.

Can I use any side as the base?

Yes! You can choose any of the three sides as the base. However, you must use the height that corresponds to that specific base - the perpendicular distance from that base to the opposite vertex.

What if I only know the three side lengths?

If you know all three sides but not the height, you can use Heron's formula: A = √(s(s-a)(s-b)(s-c)), where s is the semi-perimeter (a+b+c)/2.

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