Dust Collector CFM Chart

Most stationary woodworking machines are documented at somewhere between 300 and 900 CFM, and a 4-inch duct can only carry about 350 CFM at the velocity required to keep chips moving. Those two facts together explain nearly every disappointing dust collector. This page is the reference tables, with the source named on every figure.

It is a companion to our CFM guide, which argues the why— why a collector's free-air rating overstates what reaches the tool. This page is the what: the numbers themselves, in a form you can look one up in.

Table 1 — Published CFM by machine

These are Rockler's published figures, reproduced with attribution rather than paraphrased. They describe the airflow needed at the machine, not the collector's free-air rating.

Oneida Air Systems frames the same territory more broadly: “most woodworking equipment requires about 250–1000 CFM,” and average table saws, planers and jointers with 2–5 in. ports “need approximately 300–600 CFM to clean well.” The two sources agree, which is worth saying because plenty of charts on the web do not agree with anybody.

Machines absent from the table.A wood lathe and a router table are not on it, because we could not find a published figure for either from a source we were willing to cite. Both are awkward cases — a lathe throws material in an arc that no fixed port covers, and a router table has two collection points. We deal with them separately in lathe dust collection and router table dust collection rather than inventing a row here.

Table 2 — What each duct diameter can actually carry

This is the table that changes how people buy. Air has to move fast enough to keep wood chips suspended, or they drop out and pack the pipe. Air Handling Systems publishes the industry figures for woodworking dust: 4,000 FPM in a branch serving a machine, and 3,500 FPM in the main. Volume is then just velocity times area, so a pipe of a given diameter has a hard ceiling on the CFM it can deliver.

Where those numbers come from.They are arithmetic, and you can check every one: CFM = velocity × area, where area in square feet is π × (diameter in inches ÷ 24)². A 4-inch pipe has an area of 0.0873 sq ft; at 4,000 FPM that is 349 CFM.

We did not simply trust our own arithmetic. Air Handling Systems publishes 195 CFM for 3 in., 350 CFM for 4 in. and 550 CFM for 5 in.; Curt Corum of the same company, writing on WOODWEB, publishes 350 CFM for a 4-inch branch and 300 CFM in a 4-inch main, and 785 CFM for a 6-inch branch against 700 CFM in a 6-inch main. Our computed figures reproduce all of those within rounding, which is why we were willing to compute the 2-1/2 in., 7 in. and 8 in. rows the same way rather than leave them blank.

Reading the two tables together

Put table 1 next to table 2 and the central problem of small-shop dust collection appears immediately:

• A 12-inch planer is documented at 500 CFM. A 4-inch duct tops out at 349. The planer is starved before the collector is even switched on.
• A 10-inch table sawat 350–450 CFM sits right at the 4-inch ceiling. At the bottom of its range it works; at the top it does not.
• A drill press or scroll saw at 300 CFM is comfortably inside a 4-inch duct and would be badly served by 2-1/2 in. hose, which caps at 136.
• Everything at 500 CFM and above wants 5 or 6-inch duct to the machine. That is a ducting decision, not a horsepower decision, and it is usually the cheaper fix.

This is why our small-shop collector roundup weights airflow headroom so heavily, and why the ducting guide spends more time on diameter than on brand.

The 350 CFM number has a serious challenger

The figures in table 1 describe chip collection— clearing the visible waste a machine throws. Bill Pentz, whose dust-collection research is the most-cited independent work in the hobby, argues those numbers are far too low for capturing the fine, invisible fraction that stays airborne and does the damage to your lungs. His position is that roughly 800 CFMis needed at larger stationary tools for good fine-dust capture, against 350–450 CFM for chips, and that this requires 6-inch duct: he points out that 4-inch pipe at 4,000 FPM reduces an 800 CFM target to 349 CFM, the same arithmetic as table 2.

We are not going to pretend to adjudicate between an industry standard and a well-argued challenge to it. What we will say is which question each answers. If you want the floor clear, table 1 is your number. If you care about what is still hanging in the air an hour later — and you should, for reasons set out in wood dust health risks — Pentz's figure is the honest target, and almost nothing sold as a small-shop collector reaches it through 4-inch pipe.

Static pressure, briefly

CFM is only half the specification. The other half is static pressure — the resistance the system pushes back with, measured in inches of water column. Every foot of pipe, every elbow, every blast gate and the filter itself adds to it, and a collector delivers less air as static pressure rises. Oneida gives a worked example: a 4-inch pipe five feet long adds 0.285 in. WC, and a 6-inch duct adds about half that.

That is the mechanism behind the advice everyone repeats without explaining: shorter, wider, smoother. Each one lowers static pressure, and lower static pressure means the collector operates further up its own curve. A vac works the opposite way round — high static pressure, low volume — which is why it suits a sander port and fails on a 4-inch one. That split is the whole subject of shop vac vs dust collector.

How to size your own setup from these tables

1. Find your busiest machine in table 1 and take the top of its range.
2. Find the smallest duct diameter anywhere in the run to that machine — including the machine's own port and any reducer — and look up its ceiling in table 2.
3. If the duct ceiling is below the machine's requirement, no collector fixes it. Change the duct.
4. Only once the duct can carry the volume, buy a collector with enough headroom above that figure to survive the length, elbows and filter loading of your actual run.

What we could not verify

We have not measured airflow on any machine or any duct run — we do not have a lab, and we say so on our methodology page. Table 1 is Rockler's published figures. The velocity standards and the three cross-check figures in table 2 are Air Handling Systems' and WOODWEB's published figures. The remaining rows of table 2 are our own arithmetic from those published velocities, and we show the formula so you can check it. The 800 CFM fine-dust figure is Bill Pentz's stated position, presented as his, not ours. We found no citable published CFM figure for a wood lathe or a router table, so neither appears in table 1.