How this calculation works
The largest exradius is opposite the longest side because its denominator s−a is smallest.
rₐ = A/(s−a), rᵦ = A/(s−b), r꜀ = A/(s−c)A worked example
A 3–4–5 triangle has area 6 and semiperimeter 6, so the exradii are 2, 3 and 6.
Good to know
Use positive sides of a nondegenerate triangle.
Reference: OpenStax Algebra and Trigonometry, Trigonometric Applications (opens in a new tab) ↗
Read the result
Find all three exterior tangent circles. Each touches one side and the extensions of the other two.
The primary result is labeled “Exradius opposite A”. Keep the input definitions in view when comparing this result with another method.
Try a related calculation
Use positive sides of a nondegenerate triangle.
For a related exercise, try the circle calculator.
A few questions, answered
How can I check the default inputs by hand?
A 3–4–5 triangle has area 6 and semiperimeter 6, so the exradii are 2, 3 and 6.
Which rule does this calculator apply?
rₐ = A/(s−a), rᵦ = A/(s−b), r꜀ = A/(s−c)