- Q.In the "On the
House " column in the October 2000 issue, we described
a method for finding the radius of a circle when only an arc of
the circle is known. This problem needs to be solved when
laying out an arch-top window opening or a barrel-vaulted
ceiling.
A.Two readers, Warren Barstad of Fertile, Minn., and Peter
Hueber of Truckee, Calif., wrote to suggest that the problem
can be solved a different way, using a mathematical formula.
Here is the formula to find the radius (r) of a circle, when
presented with an arc measuring w inches wide and h inches
high: