Isosceles Triangle Side Calculator

Using the isosceles triangle side calculator is as easy as counting to three! All you need to do is:

1. Enter the known dimensions of your isosceles triangle. These can be its angles, height, or even a side if you know it.
2. Find your results filled into their respective fields.
3. The calculator can work backward, too: fill in the sides, and the calculator will work out all the other dimensions.

If you'd like to learn how the side lengths are calculated, read on!

An isosceles triangle is a triangle with two equally long sides (which we call the legs) and are both denoted with a. The remaining side is denoted by b and is unique. The angles adjacent to b (which we call the base angles α) are also equal due to the legs being equal in length. The remaining angle at the top is called the vertex angle β and is unique.

If the only unknown side is the base side b, our steps depend on what information we have. Usually, we have the leg length a, the base angle α, and the vertex angle β. We can then apply trigonometry to one half of the isosceles triangle, which is a right triangle with angles α and β/2, a hypotenuse of length a, and a side of length b/2. From there, we can calculate b/2 and then b.

If you found that this isosceles triangle side calculator isn't acute enough, might we interest you in some of our other isosceles triangle calculators?

• Isosceles triangle;
• Isosceles right triangle;
• Isosceles triangle find A;
• Isosceles triangle angles;
• Isosceles triangle area;
• Isosceles triangle height; or
• Triangle vertices.