What PSI is best for a pressure washer? Get the right amount jet strength for every job

It may sound obvious, but knowing what PSI is best for a pressure washer is fundamental to making the right purchase decision. Too little pressure and you won’t get a good clean. Too much and you could cause damage to your property or even hurt yourself.

Not all models are created equal, so knowing what is the best pressure washer for you – and the PSI or BAR pressure levels you’ll need – will largely depend on the jobs you’re intending to tackle.

Understanding PSI and BAR pressure measurements

In the pressure washer world, there are two main measures of the force exerted by the water as it leaves the nozzle: PSI, or pounds per square inch, which is the imperial equivalent of BAR, the metric unit. 1 BAR is equivalent to the pressure exerted by the earth’s atmosphere at sea level.

In simple terms, the higher the PSI or BAR, the greater the cleaning power of the pressure washer. The higher the PSI, the more effective your washer will be at removing stubborn dirt, grime and stains from surfaces. But at the same time, using a pressure washer at too high a PSI level could damage whatever you’re cleaning.

“Most pressure washers have enough operating pressure to take on a variety of cleaning tasks around the home and garden,” says Paul Hicks, marketing and product manager at Stihl GB. “Models with the highest operating pressure and water throughput capabilities will clean through the most extreme dirt quickly and easily, so will be your best bet for demanding cleaning jobs.

“Pressure washers with a lower operating pressure and water throughput are designed for lighter, more delicate cleaning jobs. They will be capable of cleaning through thick dirt, but it will take longer to do the job thoroughly, so we wouldn’t recommend using a small machine for demanding cleaning tasks.”

What are the best pressures for different cleaning jobs?

Depending on the model you choose, you may be able to manually adjust the pressure of your washer depending on the job at hand. “Opting for a washer with adjustable pressure settings is highly advised as this will help accommodate your different surfaces and give you the best flexibility when it comes to a deep clean,” explains Joshua Warren, pressure washer and floorcare expert at AO.

“Many pressure washers can be adjusted depending on the job,” adds Claire Baglin, landscaping category manager at Toolstation. This isn’t always possible, though, as some pressure washers don’t have an adjustable dial.

Together, Claire and Joshua take us through their recommendations for the right pressure level for common outdoor cleaning jobs.

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What pressure do I need to use for cleaning wood?

Wood furniture and decking can be prone to splintering, so Joshua advises using a pressure of between 1,000 and 1,500 PSI. Toolstation advises a PSI of 1,200, the equivalent of 83 BAR. This level is also suitable for more robust patio furniture, fencing and windows and doors and their frames.

“Use a 45-degree nozzle angle that will remove any stubborn dirt and algae but leave the decking surface unharmed,” adds Claire.

“Cleaning wooden garden furniture with a pressure washer is perfectly safe but can strip the furniture of its oil; make sure you re-oil your furniture as soon as it dries out to increase its lifespan” adds Paul.

If you’re looking to specifically clean your decking, we’ve got a full length ‘how to clean your decking with a pressure washer’ guide with a more detailed breakdown.

What pressure do I need to use for cleaning a car?

“Cars often require a softer touch as they have surfaces easily scratched and damaged by high pressure,” says Joshua. “For this reason, we’d recommend a pressure of 1,200 to 1,900 PSI.” This translates to 103 BAR, if we use the 1,500 PSI midpoint.

“Don’t use a nozzle below a 25-degree spray pattern and make sure to keep at least 15cm away from the surface,” says Claire.

What pressure do I need to use for cleaning a patio?

“Pavement and brick surfaces can withstand much higher pressure levels with little risk of damage, so for this you can use a pressure in the region of 2,000 to 3,000 PSI,” says Joshua. If we convert the midpoint to metric, then you’ll need to use 172 BAR.

“Use a 10- to 15-degree nozzle angle for a greater pressure. This will help to remove any dirt build-up and brighten the surface,” suggests Claire. “A specialised patio cleaning hood can also be used to stop dirty water from spraying where you don’t want it to.” For more advice, we’ve got a full guide on how to clean your patio with a pressure washer.

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“If you have sand between the stones in your patio, pressure washing could blast this away, leaving you at risk of your paving stones shifting and forming cavities,” warns Paul. “Be sure to check for this and replace the sand as soon as possible if your patio needs it.”

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What pressure do I need to use for cleaning concrete?

“2,500 to 3,500 PSI” is the pressure suggested by Joshua for this most robust of surfaces. “Like your patio, concrete can tolerate a higher pressure level,” he says. “For the best results, I’d recommend that you use a turbo nozzle or rotary surface cleaner attachment.” Again, for the midpoint, you’ll need 207 BAR to clean concrete.

What’s the best PSI for a pressure washer overall?

“If you’re a DIYer, a pressure washer with at least 3,000 PSI should cover most jobs around the home,” says Claire, who explains that it’s usually better to overcompensate a little on that maximum pressure level when shopping for a pressure washer. “This is because the PSI level can often be adjusted lower from the maximum amount of pressure to handle more delicate jobs, but it cannot be increased,” she explains.

“For example, if you bought a 1,500 PSI washer to clean your car but later wanted to clean your driveway, the pressure cannot be increased from that 1,500 PSI and so it wouldn’t be effective,” Claire adds. “Whereas if you choose a 3,000 PSI washer it can be turned down to 1,500 PSI and then back up to 3,000 PSI.”

What can affect the pressure level of my pressure washer?

“The main cause of low pressure is a blocked or worn nozzle, as both of these can cause less water to pass through. A key way to identify this is through an irregular spray pattern,” explains Claire at Toolstation.

“Another common cause can be an issue with the inlet hose, as most machines require a flow rate of at least four litres of water per minute to work properly. Make sure the garden hose has no kinks or leaks and the tap is fully open,” she advises. “The inlet filter screen should also be regularly checked to make sure no debris is blocking the water intake.”

Paul Hicks agrees: “For example, if you are cleaning a patio with thick, stubborn dirt that has built up over the winter season, you’ll need to make sure your pressure washer is receiving the right water flow so it can achieve the correct operating pressure to tackle the task,” he says. “If the pressure washer receives a disrupted waterflow, it isn’t going to reach the right operating pressure to clean the thick dirt away.”

“Different factors can affect your pressure washer,” says Joshua. “A higher water flow can result in a better clean, while different nozzles and attachments can modify the pressure and spray pattern. A key thing to note is the distance from the surface you use your pressure washer – the closer it is, the more pressure is applied.”

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What are the consequences of buying a washer that has too high or low a pressure?

“Using a pressure washer that runs too high or low can be detrimental to your cleaning efforts,” explains Joshua. “If it is too high, then this can cause damage by stripping paint, scarring concrete or splintering wood. Conversely, too low on pressure and this may not effectively remove dirt and grime, resulting in a shoddy clean.”

Claire also warns that excessively high water pressure can potentially cause physical harm to the user. “The higher force can deteriorate the surface of objects but also throw up objects that can cause more damage,” she points out.

What other features are important to consider when choosing a pressure washer?

PSI (or BAR) is only one aspect of a pressure washer’s cleaning ability. The following features are also important.

Flow rate

“It’s a good idea to look at the appliance’s flow rate [the amount of water that the washer can process each hour],” says Joshua. “A higher flow rate means a faster clean at a higher consumption of water.”

Nozzle selection

Pressure washers typically come with a choice of attachments designed for different tasks, with more specific tools available for specialist jobs. It’s crucial you read up on what each one does and make the right selection. “Otherwise you can cause damage to the item you are cleaning,” says Stihl’s Paul Hicks. “A surface cleaner will help you to thoroughly clean patios, driveways and the like, whereas a rotating roller brush attachment will help you gently clean sensitive surfaces, such as wooden terraces or garage doors, without causing damage.

“Rotary nozzles are designed for thick, stubborn dirt, spraying a high-intensity blast of water in a high-speed, zero-degree spray pattern. This is ideal for heavy-duty cleaning of thick mud, patio slabs and driveways, but if you use this powerful nozzle on wooden decking it will cause damage.

“We also have a fan jet nozzle which sprays water evenly in a fan-like motion to cover the whole surface, making it ideal for more general cleaning. It doesn’t have a high-intensity spray like the rotary nozzle, so is perfect for cleaning sensitive surfaces, such as your car or wooden decking.

“The important thing is to take care when you’re using any attachment. For example, if you’re cleaning an old plastic garden chair at proximity with a rotary nozzle and focusing on one area for too long, it can destroy the plastic and cause it to snap; instead, opt for a fan jet nozzle and evenly spray the chair.”

Hose length

“The length of a pressure washer hose starts around three metres, but can go up to more than ten metres for more expensive models,’ says Claire. “Long hoses are ideal when you need to reach far corners, such as the back corner of a large swimming pool.

“However, a longer hose could be a nuisance in small spaces – it can get damaged by kinking or snagging, and makes the washer heavier,” she warns. “I recommend only choosing hoses longer than ten metres if you regularly work in large spaces and really need the extra reach.”

Auto start/stop

“An auto start/stop trigger for your pressure washer at one end of the lance is great for saving water and reducing the time your pressure washer is on for,” says Claire. “Essentially when you pull the trigger, the water comes out. When you let go, the water stops.

“If you have a large space, a pressure washer without an auto start/stop feature, and decking at the far end of your garden to clean, you’ll have to run the water until you get there or recruit a family member to switch it on, which could get annoying,” she explains.

Battery life

“If you’re buying a cordless pressure washer, be sure to look out for washers that have a long battery life, as they will allow you to clean well for longer between charges,” says Joshua.