What PSI do I need for patio cleaning?

Concrete patios typically need 2,000-3,000 PSI for effective cleaning. Natural stone patios require lower pressure — 1,500-2,000 PSI — as higher pressure can damage soft stone. Always test in an inconspicuous area first and adjust pressure and distance accordingly.

What do the nozzle degree numbers mean?

The degree number indicates the spray angle: 0° is a pinpoint jet (very aggressive, rarely used), 15° is a narrow powerful fan, 25° is the most common general-purpose angle, 40° is a wide gentle fan, and 65° is for applying detergent. Lower angles deliver more pressure per square inch.

How far should I hold the lance from the surface?

Typically 15-40 cm depending on the surface. Harder surfaces like concrete can tolerate a closer distance (15 cm), while delicate surfaces like render or wood need 30-40 cm. Start further away and move closer gradually until you find the effective cleaning distance.

What are cleaning units (CU)?

Cleaning units (CU) are calculated by multiplying PSI by GPM (gallons per minute). This gives a single number that represents overall cleaning power. A machine with 2,500 PSI and 2.5 GPM has 6,250 CU. Higher CU means faster cleaning. Under 4,000 CU is light duty, 4,000-8,000 is medium, and 8,000+ is heavy duty.

Can too much pressure damage surfaces?

Yes, excessive pressure can damage many surfaces: it can pit concrete, erode mortar joints, splinter wood, strip paint, damage render, and remove the surface layer from tarmac. Always use the minimum pressure needed for effective cleaning and test in a hidden area first.

CleanCalcs

Pressure Washer PSI Calculator

Determine the correct PSI setting for different surfaces and cleaning tasks.

Surface Type

Your Machine Max PSI

Check your machine spec

Flow Rate

Gallons per minute from spec sheet

How We Calculate This

How the calculator works

This calculator provides recommended PSI ranges, nozzle types and standoff distances based on the surface material being cleaned.

PSI ranges by surface

Concrete: 2,000-3,000 PSI
Natural stone: 1,500-2,000 PSI
Wood decking: 1,000-1,500 PSI
Render: 800-1,200 PSI
Vehicle: 1,000-1,500 PSI

Cleaning units (CU)

Cleaning Units = PSI x GPM

Cleaning units combine pressure and flow rate into a single performance metric. Higher CU means faster, more effective cleaning. As a guide: under 4,000 CU is light duty, 4,000-8,000 CU is medium duty, and 8,000+ CU is heavy duty / professional.

The calculator also checks whether your machine has sufficient PSI for the selected surface.

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates. Always verify quantities and timings for your specific situation.