Dust Collection CFM

A dust collector only keeps your shop clean if the air in the duct moves fast enough to carry the chips all the way to the bin. That means matching the duct size to the airflow: too big and the air slows and the line clogs, too small and the machine chokes. This gives you the airflow a duct carries at a chosen velocity, or the duct size a machine's CFM needs.

It is about velocity, not just the fan

Dust collection lives or dies on air speed in the duct. Wood chips and shavings only stay airborne while the air is moving fast, so you aim for roughly 4000 feet per minute in the branch lines and about 3500 in the main trunk. Let the velocity fall below that and the heavier bits drop out and pile up until the line blocks. So the duct is not just a pipe, its size sets the speed for a given airflow, and that speed is what actually moves the dust.

Why duct size and airflow are tied

Push a fixed airflow through a bigger pipe and the air spreads out and slows down; through a smaller pipe and it speeds up but the machine fights to pull enough through. There is a sweet spot where the duct is just small enough to hold the velocity up without choking the flow. That is what this calculates: give it the airflow and it sizes the duct, or give it the duct and it tells you the airflow, both at the velocity you set.

Match the machine

Different machines make different amounts of dust and need different airflow. A table saw, bandsaw, jointer or router table is happy around 350 to 400 CFM; a thickness planer or a drum sander throws far more and wants 400 and up; a wide planer or a big lathe more still. Size the drop to the hungriest machine on it, and if one branch feeds a planer, do not starve it with a four inch hose meant for a sander.

Pay the toll for length and elbows

Every foot of duct and every bend rubs against the air and costs you flow, and flexible hose costs more than smooth pipe. A long run with several tight elbows can lose a big chunk of what the collector makes at the inlet. This figures the straight-pipe case; for a real run, give yourself margin, keep the runs short and the bends gentle, and use solid pipe where you can. Measure the velocity at the machine if you can, and resize if it has sagged.

More MakerKiln tools

• board feetBoard Foot CalculatorBoard feet and cost for a whole lumber list, with a waste allowance.→
• will it bowShelf Sag CalculatorHow much a shelf will bow under load, and whether it needs support.→
• cut listCut List OptimizerFit your parts onto boards or sheets with the least waste.→

Put this calculator on your site

Free to embed, and welcome. It runs the same way, in your visitor's browser, and it sizes itself to fit. Paste this where you want it, and it stays current on its own:

<iframe src="https://makerkiln.com/dust-collection-cfm-calculator/embed/" title="Dust Collection CFM Calculator" loading="lazy" style="width:100%;max-width:560px;height:560px;border:1px solid #d9dee8;border-radius:14px"></iframe>
<p style="font:13px/1.4 system-ui,sans-serif;margin:6px 2px">Free calculator by <a href="https://makerkiln.com/dust-collection-cfm-calculator/" target="_blank" rel="noopener">MakerKiln</a></p>
<script>window.addEventListener("message",function(e){if(e.data&&e.data.mk==="h"&&e.data.slug==="dust-collection-cfm-calculator"){var f=document.querySelector('iframe[src="https://makerkiln.com/dust-collection-cfm-calculator/embed/"]');if(f){f.style.height=e.data.h+"px"}}});</script>

Prefer to host it yourself, offline or on an intranet? Download the file above. Keep the MakerKiln credit and it is free to use.