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# How do I calculate the diameter or radius of an arc?

If you know two of the following about an arc, you can calculate the diameter or radius for that arc.

• Segment Height (rise)
• Chord Length (run) of an arc.
• Arc Angle

Here are some examples:

Example 1:
Find the radius of an arc given a Segment Height (Rise) of 2m and a Chord Length (Run) of 6m

 You Input [clr] [clr] 6 [m] [Run] 2 [m] [Rise] [Conv] [Radius]
 BuildCalc Displays 0 6m Run 6m Rise 2m Radius 3.25m

Example 2:  Find the diameter of an arc given a Segment Height (Rise) of 6ft 2in and a Chord Length (Run) of 20ft 6in

 Your Input [clr] [clr] 6 [Feet] 2 [in] [Rise] 20 [Feet] 6 [Inch] [Run] [Circle]
 BuildCalc Displays 0 6ft 2in Run 6ft 2in Rise 20ft 6in Diameter 23ft 2- 7/16in

Example 3:  Find the radius and diameter of an arc given a Chord Length (Run) of 36 inch and a 30° arc angle.

 You Input [clr] [clr] 36 [Inch] [Run] 30 [Arc] [Conv] [Radius] [Circle]
 BuildCalc Displays 0 Run 36in Arc Angle 30.00° Radius 69- 9/16in Diameter 139- 1/16in

Note that the [Arc] function can be used to calculate the length of each stud required to frame an arch.