Input Parameters
How the duct offset formula works
For two equal-angle duct transitions, the sloped length on each side is L = H ÷ sin(θ). The straight run occupied by the offset is R = H ÷ tan(θ).
This calculator gives a geometry estimate for round or rectangular ductwork. It does not size the duct cross-section or replace a shop drawing: allow for seams, fitting lengths, turning vanes, insulation, and access clearance.
Example: 12-inch offset at 30°
A 12 in offset at 30° needs 24.0 in of sloped length on each side and 20.8 in of straight run between the bends. The total sloped length is 48.0 in.
FAQ
What is a duct offset?
A parallel shift in a duct run used to clear beams, pipes, structure, or other obstructions.
What is the duct offset formula?
Each sloped side = offset ÷ sin(angle); straight run = offset ÷ tan(angle).
Is this the same as a conduit offset?
The trigonometry is similar, but duct fittings and fabrication allowances differ. Use the conduit tool for EMT, PVC, or electrical conduit.