Right Triangle Calculator (Sides, Angles, Area)
Choose what you know and enter the values.
Your numbers
Your results
Sides a, b, c
Sides a, b, c
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Angle A (degrees)
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Angle B (degrees)
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Area
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Perimeter
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Altitude to the hypotenuse
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Right Triangle Calculator (Sides, Angles, Area) by TheCalcTools
How the Right Triangle Calculator (Sides, Angles, Area) works
In a right triangle the legs and hypotenuse satisfy a² + b² = c². The angles follow from the trigonometric ratios: sin A = a/c, cos A = b/c, tan A = a/b, and the two acute angles add up to 90°.
The altitude from the right angle to the hypotenuse is ab/c, and the area is half the product of the legs.
The formula
c = √(a² + b²); A = atan(a/b); area = ab/2
Worked example
Using the default values shown in the calculator:
| I know | Both legs (a and b) |
|---|---|
| Leg a | 3 |
| Leg b | 4 |
| Hypotenuse c | 5 |
| Angle A (degrees) | 36.87 |
- Legs 3 and 4: sides 3, 4, 5.
- Angles 36.8699° and 53.1301°; area 6.0000.
Result:
| Sides a, b, c | 3, 4, 5 |
|---|---|
| Angle A (degrees) | 36.8699 |
| Angle B (degrees) | 53.1301 |
| Area | 6.0000 |
| Perimeter | 12.0000 |
| Altitude to the hypotenuse | 2.4000 |
Frequently asked questions
What is a 3-4-5 triangle?
The simplest right triangle with whole-number sides, used by builders to set out square corners.
Sources and further reading
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