Cleaning units equal PSI times GPM. See how the formula works, typical ranges by machine class, and why it beats comparing PSI alone.
Cleaning units, often abbreviated CU, are the single most useful number for comparing pressure washers, yet most shoppers never see it printed on the box. Manufacturers advertise PSI prominently because it is a bigger, more exciting number, but cleaning units give a far more honest picture of how fast and how well a machine will actually clean.
The Formula
Cleaning units are calculated by multiplying PSI by GPM. A machine rated at 2,000 PSI and 1.4 GPM produces 2,800 cleaning units. A second machine rated at 1,800 PSI but 1.6 GPM produces 2,880 cleaning units, meaning it will likely clean a large flat area faster despite the lower PSI number on the label. For the underlying explanation of why both numbers matter, see our companion piece on PSI vs GPM and what actually matters.
Why This Number Exists
PSI alone measures force, and GPM alone measures flow. Neither one describes total cleaning throughput by itself. A high-PSI, low-GPM machine can blast a stubborn spot but takes a long time to cover a driveway, because each pass removes and rinses away less material per second. A lower-PSI, higher-GPM machine spreads that same cleaning force over more water volume, clearing wider areas per pass. Cleaning units combine both into one comparable figure so you are not stuck guessing which spec matters more for your specific job.
Typical Cleaning Unit Ranges
Light-duty electric pressure washers built for cars, patio furniture, grills, and small decks typically fall between 1,500 and 2,800 cleaning units. Mid-duty electric and light gas units used for driveways, fences, and full house siding usually land between 2,800 and 4,500 cleaning units. Heavy-duty gas units aimed at large concrete areas, fleet washing, and commercial jobs often exceed 4,500 to 6,000 cleaning units, and true commercial-grade units can push past 8,000.
Matching your machine’s cleaning unit range to the job keeps you from either underpowering a big driveway project or overpowering a fragile surface like a wood deck or vinyl siding.
Where Cleaning Units Fall Short
Cleaning units are a useful shortcut, but they do not account for nozzle selection, standoff distance, or surface material, all of which change the real-world effect of the same spray. A 3,000 cleaning unit machine fitted with a 0-degree pinpoint tip held two inches from vinyl siding can gouge material that the same machine would clean safely with a 40-degree tip held two feet away. The number tells you the machine’s raw potential, not how it will behave on a specific surface with a specific nozzle.
Using Cleaning Units to Shop
When comparing two pressure washers, do the multiplication yourself if the manufacturer only lists PSI and GPM separately. Decide what you clean most often, cars and patio furniture call for the low end of the range, while concrete driveways and two-story siding call for the middle to upper range. Buying well beyond your actual needs mostly adds cost, weight, and a machine that is harder to control on delicate surfaces, since scaling down an oversized unit’s output correctly with nozzles and standoff distance takes more care than simply owning the right size to begin with.
Cleaning Units and Job Time
Beyond raw cleaning ability, cleaning units correlate closely with how long a job takes. Doubling GPM while holding PSI constant roughly doubles the water volume moving across a surface each minute, which can cut the time needed to rinse a long driveway or fence run nearly in half. This is why commercial cleaning crews prioritize GPM heavily even though PSI gets more attention in consumer marketing.
Reading Cleaning Units on a Spec Sheet
Some manufacturers list cleaning units directly, usually printed as CU on the box or spec sheet, while others force you to calculate it yourself from the separate PSI and GPM figures. When comparing two machines at similar price points, doing this quick multiplication often reveals a meaningful gap in real cleaning capacity that the headline PSI number alone would hide. A machine advertised heavily on a high PSI figure but paired with a modest GPM rating can end up with fewer total cleaning units than a competitor with a lower PSI claim but noticeably higher flow.
Cleaning Units Across a Property
Most homeowners do not clean just one type of surface, and a single machine’s cleaning unit rating has to serve everything from a car to a driveway. Choosing a mid-range cleaning unit total, rather than the highest number available, along with a full set of nozzle tips, generally gives more flexibility than buying strictly for the hardest single job on the property.
How we research
We compare published manufacturer specifications, official manuals, warranty information and recurring owner feedback. Rankings are research-based unless original YardToolLab test evidence is explicitly shown on the page.
FAQs
Multiply the PSI rating by the GPM rating listed on the pressure washer's spec sheet. A 2,300 PSI machine with 1.2 GPM produces 2,760 cleaning units. Manufacturers rarely print the total, so this quick multiplication is worth doing before buying.
Not for every job. More cleaning units means more raw cleaning power, but on delicate surfaces like wood or vinyl siding, excess power increases the risk of damage unless you use a wider nozzle and greater standoff distance to control it.
Most concrete driveways clean well in the 3,000 to 5,000 cleaning unit range paired with a 15 or 25-degree nozzle or a surface cleaner attachment. Heavily stained or oil-marked concrete may benefit from the higher end of that range.
Yes, the formula is identical for both. Gas units generally land higher in cleaning units because they produce more GPM, which is the main reason they clean large areas faster than most electric models.