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
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.