Square Foot Calculator Triangle
Calculate the square footage of a triangle. Enter the base and height to get the area in square feet using the formula ½ × Base × Height.
Triangle Area Calculator
Enter the base and perpendicular height of the triangle to calculate its area.
The height must be perpendicular
to the base (90° angle).
How to Calculate Square Footage of a Triangle
Triangles appear in roofs, gable walls, decorative elements, sail shades, and oddly shaped lots. Calculating the area of a triangle requires just two measurements: the base and the perpendicular height. This is one of the most fundamental geometry formulas and is essential for construction, landscaping, and real estate.
Triangle Area Formula
The base is any side of the triangle. The height is the perpendicular distance from that base to the opposite vertex (the highest point). The key word is perpendicular — the height must form a 90° angle with the base.
Step-by-Step Instructions
- Choose a base side — typically the bottom side of the triangle that rests on the ground.
- Measure the base length in feet from one corner to the other.
- Measure the height — drop a perpendicular line from the base to the top vertex and measure that distance.
- Multiply ½ × base × height to get the area in square feet.
Worked Examples
A triangular gable wall has a base of 20 feet and a height of 8 feet.
½ × 20 ft × 8 ft = 80 square feet (7.43 sq m)
A triangle-shaped flower bed has a base of 15 feet and a height of 6 feet.
½ × 15 ft × 6 ft = 45 square feet (4.18 sq m)
Common Uses for Triangle Area Calculations
- Roofing — calculating gable end area for siding, insulation, or shingles
- Landscaping — triangular garden beds, corner plantings, and lawn sections
- Construction — triangular wall sections, dormers, and decorative features
- Sail shades — triangular shade sails for patios and outdoor areas
- Property surveys — oddly shaped lot sections that form triangles
Alternative Methods: Heron's Formula
If you know all three side lengths but not the height, use Heron's formula:
Where a, b, c are the three side lengths and s is the semi-perimeter. This is useful when measuring the perimeter of a physical triangular area where the height is difficult to measure directly.
Triangle vs. Rectangle Comparison
| Dimension | Rectangle Area | Triangle Area |
|---|---|---|
| 10 × 8 ft | 80 sq ft | 40 sq ft |
| 15 × 10 ft | 150 sq ft | 75 sq ft |
| 20 × 12 ft | 240 sq ft | 120 sq ft |
| 25 × 15 ft | 375 sq ft | 187.5 sq ft |
A triangle with the same base and height as a rectangle always has exactly half the area of that rectangle.
Frequently Asked Questions
How do I calculate the area of a triangle in square feet? +
Use the formula: Area = ½ × Base × Height. Measure the base (any side) and the perpendicular height from that base to the opposite vertex, both in feet, then multiply and divide by 2.
What if I only know the three sides of a triangle? +
Use Heron's formula: first calculate s = (a + b + c) / 2, then Area = √(s(s-a)(s-b)(s-c)). This works for any triangle when you know all three side lengths.
How do I find the height of a triangle? +
For a physical space, measure the perpendicular distance from the base to the opposite corner. For a right triangle, one leg is the height. You can also use Height = 2 × Area ÷ Base if you know the area.
What is the square footage of a triangle with a 20 ft base and 10 ft height? +
Area = ½ × 20 × 10 = 100 square feet. This is equivalent to 9.29 square meters.
Can I use this calculator for roof area calculations? +
Yes! Triangular gable walls and roof sections are perfect for this calculator. Measure the base width and the peak height to get the area for siding, insulation, or paint estimates.