Pressure Washer PSI Guide

Pressure washer shoppers often ask how much pressure is truly necessary, and the answer depends on the specific project. The pressure produced by a power washer is measured in PSI (pounds per square inch), and requirements can vary based on the surface being cleaned. 

For example, significantly less pressure is required to clean dirt and salt from a vehicle than is needed to remove oil stains from a garage floor. Another factor that is equally important, but often overlooked, is the gallons per minute rating (GPM). This measures the volume of water the pressure washer dispenses per minute; a higher water volume results in faster cleaning. 

How Much Pressure is Required? 

When determining the desired PSI range for a pressure washer, there are two general schools of thought. The first suggests purchasing the maximum pressure that might eventually be needed. Because pressure can be dialed down to handle smaller projects, a buyer benefits from a "buy it right and buy it once" approach rather than having to upgrade later. 

If, for example, a pressure washer is initially purchased to clean a car, but is later needed to clean a driveway, remove stains, or strip paint, the PSI requirements will be very different. In such cases, a less powerful unit may not be able to handle those jobs efficiently. Please take a moment to review the chart below, which shows approximate spec ranges for different grades of pressure washers.

On the other hand, if projects will never require more than 2,500 PSI, money can be saved by choosing a 2,600 PSI pressure washer over a 4,000 PSI model. It should be remembered that pressure ranges are variable; there is not always a noticeable difference between 1,500 and 1,600 PSI. 

Furthermore, users should always start with a lower pressure recommendation and work upward, rather than starting at the top of a recommended PSI range and risking damage to the surface being cleaned. 

The pressure washer PSI chart below provides recommended PSI ratings for several common household cleaning projects.

How Much Water Flow is Required? 

While water pressure provides the power to break up stains and dirt, water volume is what flushes that debris away. 

Essentially, the more water that moves through a nozzle in a minute, the faster a surface can be cleaned. A higher GPM (gallons per minute) rating allows for quicker cleaning because there is more flowing water present to lift and carry away dirt. 

Consider a flowing garden hose; on its own, it provides enough flow for wetting a surface but lacks the pressure for deep cleaning. If a thumb is placed over the end of the hose, the resulting pressure can wash clumps of dirt off a driveway or sidewalk. This principle applies to the relationship between PSI and GPM: combining pressure (PSI) with volume (GPM) creates a highly effective cleaning tool. Pressure washers allow for this combination of high pressure and high volume to clean stubborn surfaces in record time. 

Why PSI Matters When Using Attachments 

Attachments make pressure washing more efficient and effective, and as a result, more enjoyable to use. Choosing the right accessories can make a significant difference for any cleaning project. 

For example, a surface cleaner has minimum GPM requirements in order to properly dispense water during cleaning jobs at the rated PSI. While it may be possible to use one with a pressure washer that does not meet these requirements, doing so greatly diminishes performance. This could lead to the incorrect assumption that the surface cleaner is faulty, when it simply is not being supplied with the correct volume of water. 

Similarly, choosing the proper tips and attachments directly impacts PSI results. Below is a helpful orifice sizing chart used to determine which tips can adequately deliver the desired PSI ratings. This information is essential when selecting the right spray tip for a pressure washer. 

While different tips allow for various angles of pressure, the orifice size is critical because it determines which tips will fit on a pressure washer lance. This same principle applies when attaching a turbo nozzle, extension lance, or other similar accessories. The numbers illustrated in the chart below refer to the orifice size required for the tips to attach to the pressure washer lance. For example, 4,000 PSI at 3 GPM requires an orifice size of "3" to attach properly.