Dust Collection CFM Calculator
Woodworking dust is a fire and explosion hazard, and a shop collector rated for one machine will not run three. Enter your machines and duct run to get the CFM you need and the pipe size that actually delivers it.
Results
Enter your measurements above and press Calculate.
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How this is calculated
Two separate questions decide whether a dust system works: does the collector move enough air (CFM), and does that air move fast enough inside the duct to carry chips rather than drop them (FPM).
- Tool demand = the sum of the recommended CFM for every machine running at once
- Duct loss = run length in feet x 1.2 x (4 / duct diameter), an allowance for friction and bends
- Required CFM = tool demand + duct loss, rounded up to the next 50 CFM
- Duct velocity = CFM x 144 / duct area in square inches. The 144 comes from 1,728 cubic inches per cubic foot divided by 12 inches per foot
The target is 3,500 to 4,500 feet per minute in the main run. Below 3,500 chips settle out of the airstream and start blocking horizontal runs; above 4,500 the duct wears faster, noise rises and the fan works harder for no gain. A 4 inch main is often too small for a two-machine shop: it needs about 300 CFM to reach 3,500 FPM, and most hobby collectors only reach their rated airflow through a short, straight, oversized connection. Every 90 degree elbow costs roughly the equivalent of 1 CFM of straight run.
Questions people ask
How much CFM do I need for a table saw?
A table saw typically needs 100 CFM at the port with a 4 inch duct. Adding a router or planer pushes the requirement to 250 to 300 CFM, which is beyond what a small shop collector delivers.
What duct diameter should I use?
Four inch rigid or spiral duct for most single machines. Five or six inch for long runs or multiple machines, because friction loss grows with the cube of airflow. Never reduce duct size to fit an existing port — that is the single biggest cause of inadequate dust collection.
Why is my dust collector noisy and barely collecting?
Usually too much duct run, too many elbows, or a restricted filter. Every elbow costs roughly as much CFM as several feet of straight pipe. A cyclone separator dramatically reduces filter loading and the resulting static pressure loss.
Is wood dust explosive?
Yes. Finely airborne sawdust ignites readily at the right concentration, and collectors are a documented cause of shop fires. Use a motor rated for the duty, keep the collector outdoors or above the floor, and install a spark arrestor on the exhaust.
Should I run the dust collector constantly?
Running it a minute before and after each cut keeps the air clear and prevents the filter from clogging during the cut itself. Leaving it on continuously just heats the motor unnecessarily.
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