Pa, air watts and the suction myth
The number has tripled in three years. Your carpets have not changed.
Every listing leads with it. 8,000 Pa. 22,000 Pa. 35,000 Pa. The number has roughly tripled in three years, and the floors in your house have not changed at all. Here is what it actually measures and what it does not.
What Pa is
A pascal measures pressure. In vacuum terms it is the difference in static pressure the motor can create in a sealed test with no brush fitted. It tells you how hard the machine can pull against a closed opening. It does not tell you how much air it moves, how well it seals against your floor, or what the brush does to lift dirt out of carpet fibres.
Why the number stopped being useful
Two vacuums rated at the same Pa can perform very differently, because cleaning is a system. Airflow moves debris; brush agitation lifts what is embedded; the seal between the unit and the floor determines how much of the pressure reaches the dirt; the number of passes determines how much gets picked up at all.
A machine with lower Pa, a well-designed brush and a good floor seal will outperform a higher-Pa machine with a poor brush on the same carpet. That is not a marginal effect — it is the main effect.
What you actually need
| Your floors | Genuinely sufficient |
|---|---|
| Hard floors only | 4,000–8,000 Pa |
| Hard floors + low-pile rugs | 7,000–12,000 Pa |
| Medium-pile carpet | 10,000–18,000 Pa |
| Thick or high-pile carpet | 18,000–25,000 Pa |
| Thick carpet + heavy shedding pet | 25,000 Pa+ |
Note the top row. On hard floors, suction beyond about 8,000 Pa buys nothing except noise and shorter battery life, because there is nothing embedded to pull out — debris is simply sitting on a surface.
Work out your band
Enter your floor type, pets and household size to see the minimum useful suction — and where the extra money should go instead.
Open the suction calculator →The other units
Air watts (AW) combines airflow and suction into a single figure and is a better indicator of cleaning power. It is used mainly for upright and cordless vacuums, not robots.
CFM measures airflow volume — how much air moves per minute. High airflow with moderate pressure often cleans better than the reverse.
Water lift is the same measurement as Pa expressed differently, common in North America.
Robot vacuums use Pa almost exclusively, which is convenient for marketing precisely because it produces the largest-looking number.
What the extra money buys instead
If you have identified your band and are choosing between models, the features that change daily experience are, roughly in order:
- Navigation quality — whether it maps properly and avoids obstacles
- Brush design — whether you spend Sundays cutting hair off a roller
- Dock automation — whether you empty it weekly or monthly
- Physical height — whether it reaches under your furniture at all
- Filtration — whether it returns fine dust to the room
Suction appears nowhere on that list above your band, which is the entire point.
Carpet boost
More useful than a high headline figure. Carpet boost detects the change in surface and raises power automatically, so the machine runs quietly and efficiently on hard floors and only draws maximum power where it helps. A model with 15,000 Pa and reliable carpet detection will usually beat a 25,000 Pa model that runs at one level everywhere.
Once you know your band, the useful comparison is between models that meet it — not between headline Pa figures. Compare robot vacuums → Advertising — we may earn a commission.
Common questions
How many Pa is good for a robot vacuum?
It depends entirely on your floors. Hard floors need only 4,000–8,000 Pa. Medium carpet benefits from 10,000–18,000. Only thick carpet with heavy pet shedding justifies 25,000 Pa or more.
Is higher Pa always better?
No. Above the band your floors require, extra suction adds noise and drains battery without cleaning better. Brush design, navigation and number of passes matter far more.
What is the difference between Pa and air watts?
Pa measures static pressure in a sealed test. Air watts combines pressure with airflow and is a better indicator of real cleaning power, but robot vacuums almost always advertise Pa because it produces a larger number.
Does high suction damage carpet?
Not in normal use. The practical downsides of running maximum suction unnecessarily are noise, reduced battery life and faster brush wear rather than damage to flooring.