What PSI Pressure Washer Do I Need? A Quick Guide by Surface

PSI and Bar — What the Numbers Mean

PSI (pounds per square inch) and bar are both measurements of water pressure. Most UK machines are rated in bar, while guides often reference PSI. The conversion is straightforward: 1 bar = 14.5 PSI.

A domestic pressure washer typically operates between 100-130 bar (1,450-1,900 PSI). Commercial and professional hire machines operate between 150-250 bar (2,175-3,600 PSI). The difference isn’t incremental — a commercial machine doesn’t just clean slightly better. It cleans meaningfully faster and handles staining that domestic machines simply can’t shift.

Surface-by-Surface PSI Guide

Vehicles, garden furniture, bikes — 1,000-1,500 PSI

Light duty. A standard domestic or the lowest hire machine handles this easily. Low pressure protects paintwork and plastic. Keep the lance at least 30cm from the surface.

Patios (natural stone, Indian sandstone, slate) — 1,500-1,800 PSI

Medium-light duty. Enough to remove moss, algae, and surface dirt without cutting into softer stones. Indian sandstone in particular is easily etched by excessive pressure — start lower and increase gradually.

Patios (porcelain, concrete pavers) — 1,800-2,200 PSI

Medium duty. Porcelain and concrete pavers are harder surfaces and tolerate higher pressure well. This range removes most dirt and biological growth in a single pass.

Driveways (block paving, concrete) — 2,000-2,500 PSI

Medium-heavy duty. Driveways accumulate heavier contamination — tyre marks, oil spots, and embedded grime — that needs more pressure to shift. A rotary surface cleaner attachment is ideal here for even coverage.

Concrete (industrial, commercial) — 2,500-3,000 PSI

Heavy duty. Warehouse floors, loading bays, and commercial yards with ground-in oil and grease need the upper end of the pressure range. Petrol machines excel here.

Render, brick, masonry — 1,500-2,000 PSI (with caution)

Variable. Painted render can be stripped by pressure above 1,500 PSI. Unpainted masonry tolerates 2,000 PSI. Old or damaged pointing can be washed out at any pressure. Always test an inconspicuous area first, and use a wide fan nozzle rather than a zero-degree jet.

Decking (timber) — 1,200-1,800 PSI

Requires care. Wood fibres can be raised and damaged by excessive pressure. Use a wide fan nozzle, maintain at least 30cm distance, and follow the grain direction. A single pass is usually enough — repeated passes over the same spot cause damage.

Nozzle Choice Matters as Much as PSI

Most pressure washers come with interchangeable nozzles (colour-coded by spray angle):

Red (0 degrees): Pencil jet. Maximum impact on a tiny area. Only for extremely stubborn stains or paint stripping. Never use on stone, wood, or painted surfaces.

Yellow (15 degrees): Narrow fan. Good for heavy cleaning on hard surfaces like concrete.

Green (25 degrees): Medium fan. The most versatile nozzle. Good for general surface cleaning — patios, driveways, walls.

White (40 degrees): Wide fan. Gentle cleaning. Best for wood, delicate stone, and rinsing.

Black (low pressure): Detergent application only. No cleaning power — used to apply soap before a pressure rinse.

Common PSI Mistakes

Using a zero-degree nozzle on a patio. The pencil jet focuses all pressure on a point the size of a coin. This etches lines into stone, strips paint, and damages grout. Use 25-degree or wider for surface cleaning.

Holding the lance too close. Effective cleaning distance is 15-30cm for most jobs. Closer than 10cm concentrates pressure dangerously — even a moderate PSI setting becomes destructive at point-blank range.

Pressure washing old pointing. The mortar between bricks and pavers can be soft or crumbling. Pressure washing blasts it out, leaving gaps that let water in and accelerate further damage.

Cleaning upward on walls. Work from the bottom up when cleaning walls and render. Top-down cleaning drives dirty water under cladding, into joints, and behind render that may not be fully sealed.

Which Hireload Machine Matches Your Job

For patios, furniture, and light cleaning: Electric 240V pressure washer. Runs from a standard plug, quiet operation, 1,500-1,800 PSI. Ideal for residential garden work.

For driveways, decking, and moderate cleaning: Karcher HD 5/11 Cage. Commercial-grade from a 240V supply, consistent pressure, reliable on half-day and full-day jobs.

For heavy-duty, commercial, and oil removal: Petrol pressure washer 2,450 PSI. Maximum cleaning power in the hire range. Best for concrete, commercial yards, and tough contamination.

Related guides: How to pressure wash a patio | How to clean a driveway | Can you pressure wash decking? | 5 pressure washing mistakes