Calculating Radius of a Curve

Two points define a straight line. But 3 points define a curve. Given the distance from point A to B and the distance from B to C and the distance from A to C, this program calculates the radius of the curve defined by those 3 points. It uses the law of cosines to find the dimensions of two right triangles defined by the points, and from them, the distance to the radius center.

Enter the dimensions described in the photo. WARNING: Measurements must be extremely accurate! A small error in any measurement will cause a large error in the result. Hint: Drive a small finishing nail into each stake. Use these nails as an exact point of reference. The radius derived from this program can be used to build track panels to fit the curve.

Note: All units must be the same. (feet, inches, meters, whatever)

Curve Radius Calculator

  Distance from A to B
  Distance from B to C
  Distance from A to C
Radius of Curve... (select box to solve)