📐 Right Triangle Calculator
A right triangle is fully determined by one side and one acute angle: sine, cosine and tangent link the sides to the angles, and the third angle is simply 90° minus the one you know. Surveyors and navigators solve triangles this way every day.
Enter the known side length, the acute angle in degrees, and tell the calculator which side you gave it — the side opposite the angle, the side next to it, or the hypotenuse.
How to use this calculator
Enter one side length and one acute angle, tell the calculator which side you entered, and press Calculate.
- Type the known side length into the Known side length field.
- Type one acute angle in degrees into the Acute angle field; it must be between 0 and 90.
- Pick which side you entered: the hypotenuse, the side opposite the angle, or the side adjacent to it.
- Press Calculate to solve the whole triangle: all sides, all angles, area and perimeter.
Frequently asked questions
What does this right triangle calculator solve?
From one side and one acute angle it finds everything: the other two sides via sine, cosine and tangent, the remaining angles (90 minus your angle, and the 90-degree corner), plus the area and perimeter.
What do opposite, adjacent and hypotenuse mean?
The hypotenuse is the longest side, across from the right angle. The opposite side sits across from your chosen acute angle, and the adjacent side runs alongside it, connecting the angle to the right corner.
Can you show a worked example?
Enter hypotenuse 10 and angle 30 degrees. The opposite side is 10 times sin(30) = 5, the adjacent side is 10 times cos(30) = 8.66, and the other acute angle is 60 degrees.
Are angles in degrees or radians?
Degrees. Enter 30 for thirty degrees, not 0.524 radians.