Creating arc to exact dimensions


I’m trying to create an arc based off of a construction drawing I have. On the drawing, they give me the angle of the arc, 72.56 degrees, as well as the overall length of the face of the arc, which is 104’-0". I can’t seem to recreate this arc in Sketchup Pro. When I enter the 104’ in as the radius, it is too large. If I enter in 52’, half of the total length, as the radius, it is too small. I’m sure it’s something mathematical I’m missing, but any ideas?


Like so?

Via the yellow pad & calculator method…

72.56° is to 360° as 104’ is to (circumference)
(360 x 104) / 72.56 = 515.987 = circumference
circumference / π = radius
515.987 / 3.14159 = 82.12191 = radius


What @Geo illustrated but didn’t state is that the arc length along the curve is the product of the angle (in radians) and the radius. So you need to calculate the radius as 104/(72.56 * pi/180) = 82.122


That worked, thank you so much!