Common Rafter Calculator Instructions
Calculating the length for common rafters on a pole barn, or any other building, is easy by entering the width of the barn, the pitch of the roof, and the thickness of the ridge. The results automatically fired include the length of the rafter, the rise, and the run. Either use feet inches and fraction (25′ 6 1/4″), inches and fraction (306 1/4″), or a decimal value (306.25) can be entered in the inches box. Metric values are returned automatically.
Know that the width of the roof means outside to outside of the walls where the rafters will sit, that the roof pitch can be determined from the blueprints, and the thickness of the ridge should be known.