Duct Reducer Length Planner
Estimate a reducer transition length from inlet/outlet dimensions and make the angle assumption visible before fabrication.
Reducer inputs
Reducer length
Reducer length methodology
The simplified planning model assumes the largest dimensional change controls the side slope. The selected included angle controls how long the fitting needs to be to make that change.
Why angle sensitivity matters
A shallow reducer takes more distance to make the same dimensional change. Testing several angles is useful during layout because a change in fitting length can affect available ceiling or plant-room space.
Worked example
For a 900 × 500 mm inlet reducing to 600 × 400 mm, the largest change is 300 mm. The selected 20° included angle is then used to estimate the transition length.
Limitations
This does not create a shop-ready flat pattern, determine fitting reinforcement, or establish airflow or pressure-drop compliance.
Frequently Asked Questions
Can the outlet be larger than the inlet?
Yes. Absolute dimensional change is used.
Can I compare angles?
Yes. Recalculate using a different angle.