Fixed Ridge Height
Rafter Calculator

Math Notes and Diagrams
Imperial Units Rafter Calculator
JLC Thread ... Fixed Ridge Height and Rafter Pitch
JLC Thread ... The math, please
x =
y =
Plate Width =
design to ...
enter Design Value ...
x + Plate Width ... x1 =
y Heel Height ... y1 =
y Plumb Cut ... y2 =
Rafter Length =
Rafter Depth ... r =
Plumb Cut Depth =
Heel Height (HAP) =
Plumb Cut Depth HAP =
% material remaining =
arctan (y1/x1) ... θ =
Rise over 12 =
Check Rafter Pitch Angle
arctan (y2/x) ... θ =
Check Plumb Seat Depth
Plate Width tan θ =
Diagonal Calculations
origin to ridge (x, y)
(x + y ) =
arctan (y/x) ... φ =
Diagonal Angle =
Check Rafter Pitch Angle
φ Diagonal Angle =
Circle Calculations
center at ridge (x, y)
Radius ... R =
Distances from Ridge (x, y)
to Point of Tangency with r
Δ x =
Δ y =
Distances from Origin to
Point of Tangency with r
*x =
*y =
Check Rafter Depth
(*x + *y ) ... r =
Check Rafter Pitch Angle
arctan (Δ yx) ... θ =
arccos calculation ... θ =

Dimensions and Angles of Rafter to Fixed Point or Ridge Height
Joe Bartok