How much CFM do I need?

It depends on the largest machine: table saw needs ~350 CFM at the port, thicknesser ~500 CFM, and wide planers ~800 CFM. For a home workshop running one machine at a time, size for the largest machine.

What duct diameter should I use?

Main duct should be at least 100mm (4") for most home workshops. Use 125mm (5") if you have a thicknesser or large planer. Never reduce below the machine port size as this restricts airflow.

Is a single-stage or two-stage collector better?

Two-stage collectors (with a cyclone separator) are much better. They capture 99% of dust before it reaches the filter, extending filter life and improving suction. Single-stage collectors clog filters quickly.

WoodCalcs.uk

Dust Collection Calculator — Workshop Extraction

Calculate CFM requirements and duct sizing for workshop dust extraction.

Largest Dust PortPick the port diameter of your biggest machine — the system is sized for the largest tool running at a time.

Total Duct Length

Total length of ducting from the dust collector to the machine, including flexible hose (count flex hose as about 3× its straight length).

How We Calculate This

CFM requirements are based on the dust port size of the largest machine. The system must maintain adequate air velocity to keep wood dust suspended — typically 4000 feet per minute in the branch ducts and 3500 FPM in the main duct (the branch runs faster so material accelerates before merging into the main).

Duct-friction loss ≈ 0.5 inches WC per 3 metres of straight duct. This figure is the straight-duct friction only — add roughly 2″ WC for the collector's filter, plus losses for each elbow and any flexible hose (count flex hose as about 3× its straight length), to get the total static pressure your collector must overcome.

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates. Always verify measurements and material quantities before cutting or purchasing.