Dust Collector CFM Calculator

Inputs

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Diameter of the open tool port or branch inlet that needs enough air velocity to carry chips and dust.
in
Diameter of the duct being checked after combining active branches and airflow allowance.
in
Number of same-size tool branches expected to be open at the same time.
open
Target duct air speed used to keep chips and dust moving through the branch.
ft/min
Extra CFM added for filter loading, separator loss, small leaks and measurement uncertainty.
%

Results

Default result
Edit inputs
Collector airflow(Q_collector)
401.4cfm
Pass

branch airflow x open branches x allowance

Also computed

Branch airflow(Q_branch)Pass349.1cfm

one tool port at the target transport velocity

Main duct velocity(v_main)Pass4,600ft/min

typical woodworking dust-duct transport screen

Target velocity(v_t)4,000ft/min

typical woodworking dust-duct transport screen

Branches used(N)1open

Allowance used(M)15%

Tool port area(A_port)0.08727ft²

Dust collector airflow previewDust collector airflow previewPort area x transport velocity gives branch CFMtoolcollectorbranch flowmain duct velocityCFM with allowancePreview is an airflow screen only; final sizing needs actual static pressure, filter condition, separator loss, blast gates and fan curve.
Method notes 4 notes
  • Branch airflow = port area x target transport velocity.
  • Collector airflow = branch airflow x open branches x (1 + airflow allowance / 100).
  • Main duct velocity is recalculated from the collector airflow and main duct area. If the main is much larger than the branch, velocity can fall even when branch CFM looks acceptable.
  • Final dust-collector sizing still needs static pressure from duct length, fittings, flex hose, separator, filter condition, blast gates and the actual fan curve.

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