Square Foot Calculator Right Triangle
Calculate the square footage of a right triangle. Enter the two legs to get the area in square feet using the formula ½ × Leg A × Leg B.
Right Triangle Area Calculator
Enter the two perpendicular legs of the right triangle.
The right angle (90°) is marked
at the corner where the legs meet.
How to Calculate Square Footage of a Right Triangle
A right triangle has exactly one 90-degree angle. The two sides forming the right angle are called legs. The area formula is simplified because the legs directly serve as the base and height, making this the easiest triangle to calculate.
Right Triangle Area Formula
Leg A and Leg B are the two sides that form the 90° angle. The hypotenuse (longest side, opposite the right angle) is not needed for area calculation.
Step-by-Step Instructions
- Identify the right angle — the 90° corner of the triangle (the square corner).
- Measure Leg A — one side touching the right angle (typically the base).
- Measure Leg B — the other side touching the right angle (the height).
- Calculate: ½ × Leg A × Leg B = area in square feet.
Worked Examples
The space under a staircase forms a right triangle with legs of 12 ft (horizontal) and 9 ft (vertical).
½ × 12 × 9 = 54 square feet (5.02 sq m)
A right-triangular corner of a lot has legs of 20 ft and 15 ft.
½ × 20 × 15 = 150 square feet (13.94 sq m)
Pythagorean Theorem
While not needed for area, the Pythagorean theorem helps find the hypotenuse length. Common Pythagorean triples include 3-4-5, 5-12-13, and 8-15-17.
Common Uses
- Under-staircase storage — calculate usable floor area
- Corner cutoffs — rooms with angled corners or chamfered walls
- Roof rake areas — triangular sections where the roof meets the wall
- Diagonal garden beds — corner planting areas in rectangular yards
- Construction — bracing, diagonal supports, and angled wall sections
Common Right Triangle Sizes
| Leg A | Leg B | Area (sq ft) | Hypotenuse |
|---|---|---|---|
| 3 ft | 4 ft | 6 sq ft | 5 ft |
| 6 ft | 8 ft | 24 sq ft | 10 ft |
| 5 ft | 12 ft | 30 sq ft | 13 ft |
| 10 ft | 10 ft | 50 sq ft | 14.14 ft |
| 15 ft | 20 ft | 150 sq ft | 25 ft |
Frequently Asked Questions
How do I calculate the area of a right triangle? +
Multiply the two legs (the sides forming the 90° angle) and divide by 2: Area = ½ × Leg A × Leg B. The hypotenuse is not needed.
What is the difference between a right triangle and a regular triangle? +
A right triangle has exactly one 90° angle. The two sides forming this angle are called legs, and the longest side (opposite the right angle) is the hypotenuse.
How do I find the hypotenuse of a right triangle? +
Use the Pythagorean theorem: Hypotenuse = √(Leg A² + Leg B²). For example, legs of 3 and 4 give a hypotenuse of √(9+16) = √25 = 5.
What is the area of a right triangle with legs of 6 and 8 feet? +
Area = ½ × 6 × 8 = 24 square feet. The hypotenuse would be 10 feet (a 3-4-5 triangle scaled by 2).
When do I need a right triangle calculator? +
Use it for staircase areas, roof rake calculations, corner cutoffs in rooms, diagonal garden sections, and any area that forms a perfect right angle at one corner.