Get the area of a right angle triangle in seconds.
The area of a right angle triangle is half the product of its two perpendicular side lengths. Enter the two legs (the sides that meet at the 90° angle), and the calculator returns the area in your selected units.
- Step 1: Enter Leg A (one side forming the right angle).
- Step 2: Enter Leg B (the other perpendicular side).
- Step 3: Choose the input unit (mm, cm, m, or in).
- Step 4: Click Calculate to see the area.
- Step 5: Use Reset to clear values and try another triangle.
Core formula: area of a right angle triangle
A right angle triangle has one 90° corner. The two sides that touch at the 90° angle are called legs (they are perpendicular).
The area formula is:
| Quantity | Formula |
|---|---|
| Area (A) | A = (1/2) × a × b |
| Legs | a and b are the two perpendicular side lengths |
So if you know a and b, you can compute the area directly without needing the hypotenuse.
What the variables mean (and what to avoid)
Leg A and Leg B
Leg A and Leg B must be the two sides that form the right angle. If you accidentally use the hypotenuse (the longest side opposite 90°), the result will be wrong.
Units and why area units are squared
If your legs are in centimeters, the area comes out in square centimeters. This is because area measures “how many square units fit inside,” so units get squared.
Valid input rules
Leg lengths must be greater than 0. The calculator rejects negative numbers and non-numeric entries to prevent misleading results.
How to use this calculator correctly
- Measure or identify the two perpendicular sides that meet at the 90° angle.
- Type those lengths into the two input boxes.
- Select the unit that matches your measurements (mm, cm, m, or inches).
- Click Calculate to compute the area.
- Read the result labeled in square units.
If you’re working from a drawing, double-check which sides are perpendicular. Many geometry problems provide the legs explicitly, but real-world measurements can be misread.
Practical examples
Example 1: Flooring a small corner
Suppose you have a right-angled corner to cover with tile. The legs measure 40 cm and 30 cm. The area is:
A = (1/2) × 40 × 30 = 600 cm².
So you need enough tile to cover 600 square centimeters (plus waste, depending on your cutting and layout).
Example 2: Finding the area of a triangular garden bed
A triangular garden bed forms a right angle. One leg is 2.5 m and the other is 1.2 m. The area is:
A = (1/2) × 2.5 × 1.2 = 1.5 m².
Now you can estimate soil volume or seed coverage using area-based rates.
Frequently Asked Questions
What is the formula for the Area of a Right Angle Triangle Calculator?
The area of a right angle triangle is computed using A = (1/2) × a × b, where a and b are the two perpendicular legs. The calculator multiplies the legs, divides by two, and reports the result in square units.
Do I need the hypotenuse to find the area?
No. The area depends only on the two legs that meet at the 90° angle. Since the legs are perpendicular, the formula uses (1/2) × leg A × leg B. The hypotenuse is not required for this specific area calculation.
What unit should I use for the answer?
Use the squared version of your input unit. If your legs are entered in centimeters, the calculator outputs square centimeters (cm²). If you enter meters, the area is in square meters (m²). This keeps the result consistent with area measurement.
What if my measurements are in mixed units?
Convert them to the same unit before entering values. For example, if one leg is in inches and the other is in centimeters, convert one so both match. The calculator assumes both legs use the selected unit, ensuring correct area units.
Why does the calculator reject negative or zero values?
Triangle legs represent physical lengths, so they must be positive. A zero or negative input would imply an invalid triangle. The calculator highlights the field and shows an error message so you can correct the value and compute a meaningful area.
Quick reference
| Given | Find | Method |
|---|---|---|
| Two perpendicular legs (a, b) | Area | A = (1/2) × a × b |
| Legs in any supported unit | Area in square units | Convert lengths, then square units automatically via the calculator |
Use the calculator for fast, accurate area results, and rely on the formula when you need to show your work or verify an answer.