Pressure Washer Cleaning Unit Calculator
Cleaning Units (CU) measure the effective cleaning power of a pressure washer by combining
pressure (PSI) and flow rate (GPM). This calculator determines CU from your equipment specs
and recommends the right power level for each surface type.
Equipment Specifications
Pressure (PSI)
PSI
Flow Rate (GPM)
GPM
Target Surface
Vehicle / Boat
Wood Deck / Fence
Vinyl / Aluminum Siding
Concrete / Driveway
Brick / Stone
Commercial / Industrial
Calculate
Cleaning Units
Higher GPM (flow rate) is generally more important than raw PSI
for cleaning efficiency. CU is a useful comparison metric, but nozzle choice, distance,
and dwell time also significantly affect results.
Cleaning Units by Surface Type
| Surface | Recommended CU | Max PSI | Notes |
|---|---|---|---|
| Vehicles / Boats | 3,000–6,000 | 1,500 | Use wide fan nozzle (40°) |
| Wood Deck / Fence | 6,000–10,000 | 2,000 | Risk of wood damage above 2,000 PSI |
| Vinyl Siding | 6,000–10,000 | 2,500 | Start low, test inconspicuous area |
| Concrete Driveway | 10,000–15,000 | 3,500 | Surface cleaner attachment recommended |
| Brick / Stone | 10,000–15,000 | 3,000 | Avoid mortar joints at close range |
| Commercial / Grease | 15,000–25,000+ | 4,000+ | Hot water preferred for grease |
The Cleaning Unit Formula
Cleaning Units = PSI × GPM
Example: A 3,000 PSI machine at 2.5 GPM produces 7,500 CU. A 2,000 PSI machine at
4.0 GPM produces 8,000 CU — more effective despite lower pressure, because the higher
flow rate rinses debris more efficiently.
Frequently Asked Questions
Is higher PSI always better?
No. Excessive PSI damages soft surfaces (wood, vinyl, paint, stucco). For most residential
work, 2,000–3,000 PSI is sufficient. GPM (flow rate) matters more for cleaning speed
and rinsing power.
What is the difference between gas and electric pressure washers?
Electric units typically produce 1,500–2,300 PSI at 1.2–1.8 GPM (2,000–4,000 CU) —
adequate for vehicles, patios, and light cleaning. Gas units produce 2,500–4,000+ PSI
at 2.0–4.0 GPM (6,000–16,000 CU) — needed for concrete, commercial work, and
heavy staining.
References
- AB 1978 (2016), Property Service Workers Protection Act — California Legislative Information
- 20 to 30 percent of conditioned air is lost through leaks, holes, and poorly connected ducts
- Uniform Commercial Code — Cornell Legal Information Institute
- Uniform Commercial Code — Article 1 (General Provisions), Legal Information Institute, Cornell Law S
- Clean Water Act, 33 U.S.C. § 1251 et seq. — Cornell Legal Information Institute
- University of Washington — Pacific Northwest Extension: Roof Moss Control
- CDC — Asthma: Triggers and Indoor Environments
- CDC — Mosquito Control: Standing Water