# 45 45 90 Special Right Triangle Calculator

Enter any known value for a 45 45 90 triangle to calculate the edge lengths, altitude, area, perimeter, inradius, and circumradius.

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## What is a 45 45 90 Triangle?

A 45 45 90 triangle is a special right triangle that has two 45° interior angles and one 90° interior angle. A 45 45 90 triangle is a right triangle and is also an isosceles triangle.

You can also think of a 45 45 90 triangle as half of a square divided from one corner to the opposite corner.

## 45 45 90 Triangle Formulas

Since a 45 45 90 triangle is a special right triangle, the formulas used to calculate parts of a right triangle can be used, substituting the angles measurements.

### Solve the Hypotenuse

Given a known leg length, the hypotenuse can be solved using the Pythagorean theorem. Thus, the formula to solve the hypotenuse is:

c = a² + b²

The hypotenuse *c* is equal to the square root of leg *a* squared plus leg *b* squared. Note that in a 45 45 90 triangle legs *a* and *b* are the same length.

This formula can be simplified a bit to the following:

c = a√2

The hypotenuse *c* is equal to leg *a* times the square root of 2.

### Solve the Leg

Given the hypotenuse, the legs can be solved using the Pythagorean theorem in a slightly different way.

a = b = c√2 / 2

The legs *a* and *b* are equal to the hypotenuse *c* times the square root of 2, divided by 2.

Alternatively, the legs can be solved using 45° angle and hypotenuse with the formula below.

a = b = c × sin(45°)

The legs *a* and *b* are equal to the hypotenuse *c* times the sin of the 45° angle.

### Solve the Area

The area of a 45 45 90 triangle can be solved with the formula:

T = 2a / 2

Thus, the area *T* is equal to 2 times leg *a*, divided by 2

### Solve the Perimeter

Use this formula to calculate the perimeter:

p = 2a + c

Thus, the perimeter *p* is equal to 2 times leg *a* plus hypotenuse *c*.

For more special right triangle formulas, try our 30 60 90 calculator.