What does CADR actually measure?

CADR is the single most useful number for comparing air purifiers, and it’s worth understanding exactly what it represents.

The measurement itself

CADR — clean air delivery rate — states how much filtered air a purifier delivers per hour, typically in m³/h. It accounts for both airflow volume and how effectively the filter actually captures particles, which is why it’s more informative than either figure alone.

It’s usually measured near maximum speed

Xiaomi’s 230 m (755 ft)³/h CADR figure for the Smart Air Purifier 4 Compact, like most CADR figures in this category, is very likely measured close to the unit’s maximum fan speed — run on a quieter, lower setting, effective clearing speed is meaningfully lower.

Different purifiers may test it differently

Not every manufacturer states their testing methodology, and Dyson’s Purifier Cool PC1 doesn’t publish a CADR figure at all — relying instead on a particle-removal percentage claim, which measures something different and isn’t directly comparable to a CADR number.

Use it alongside room size, not alone

A CADR figure is most useful compared against your actual room’s air volume, not just floor area — see our guide on reading a CADR figure for the full reasoning on sizing correctly.

What we would not do

Treat CADR figures from different brands as perfectly interchangeable without checking test conditions. It’s the best comparison tool available in this category, not a perfectly standardized one across every manufacturer.

Check your own manual before you follow anything here. Humidity ranges, wattages, voltage and current ratings differ from model to model, and the manufacturer's figures take precedence over anything written on this site. We report what makers and monitors publish — a target humidity percentage, a heater's tip-over and overheat protection, a plug or thermostat's maximum load rating — and we never turn a reading into a health verdict or a diagnosis. Questions about air quality and health are matters for a qualified professional and your national health authority, and this site points you to them rather than restating them. Where wiring, voltage or load ratings are involved, matching them exactly to your appliance is a safety matter, not a technicality.