What does CFM mean on a commercial vacuum?

What CFM actually measures

A vacuum cleans by moving air. CFM is the volume of that air — cubic feet per minute — and it governs how much debris the machine can carry and how fast it carries it. Airflow is what sweeps grit off a hard floor and up a wand, and what keeps a load of dust moving rather than settling in the hose.

It is not the same as suction. Suction, quoted as water lift or as kilopascals, is the negative pressure the motor can generate — the pull it has when the air path is restricted, as it is deep in carpet pile or under water. Airflow and water lift trade against each other in the design of a motor, and a spec sheet that gives you only one of them is telling you half the story.

CFM, litres per second, and Australian spec sheets

CFM is an imperial unit and most Australian machines are specified in litres per second instead. The conversion is straightforward: one litre per second is about 2.12 CFM, so 100 CFM is roughly 47 litres per second. The POLIVAC Koala backpack is rated at 52 litres per second, which is a little over 110 CFM; the Wombat canister is 45.5 litres per second, around 96 CFM. Some machines are quoted in cubic metres per minute again — the NH007 stick vacuum is listed at 1.1 m³/min, close to 39 CFM.

The practical consequence is that comparing two machines usually means converting first, and comparing like with like second. An airflow figure measured at the motor, with nothing attached, is always higher than the airflow reaching the end of a hose, a wand and a floor tool. Two machines are only comparable if their figures were taken at the same point.

Why it beats wattage

Motor wattage describes electricity consumed, not work done. A poorly matched fan, a restrictive hose or a clogged filter will burn the same watts and move far less air. Airflow is measured at the output, so it reflects what the machine can actually do — which is why it is the number worth asking for when a supplier leads with watts.

When it matters

Reach for the CFM figure when you are comparing dry vacuums for open-floor work — corridors, classrooms, offices, warehouse aisles — where the machine spends its life picking up light debris across distance. Higher airflow moves more material per pass and is the difference between one pass and three.

Weight water lift more heavily when the air path is going to be restricted. Deep-pile carpet, wet pick-up and anything with a narrow tool on the end needs the pressure to pull through the restriction; raw airflow will not help if the machine cannot generate the vacuum to reach the soil in the first place. For most commercial buying decisions you want both numbers, not one.

What people get wrong is treating airflow as a fixed property of the machine. It is not: a full bag, a blocked pre-motor filter or a crushed hose all drop real airflow well below the rating, sometimes by half, and a machine that has lost its airflow feels like it has lost its suction. Before concluding that a vacuum is underpowered, change the bag and check the filters.