Overview PW 101, Standard For Testing And Rating Performance Of Pressure Washers: Determination Of Pressure And Water Flow & Certification Program

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Consumers use pressure washers for cleaning exterior surfaces such as decks, driveways, concrete floors, siding, fences, cars, boats, RVs, etc. To ensure the proper selection of a pressure washer, consumers need to understand pressure washer performance.

A pressure washer’s performance is rated by pounds per square inch or PSI, and gallons per minute or GPM. PSI measures pressure and GPM measures flow rate. A pressure washer’s PSI rating is the maximum amount of force (pressure) developed by the pressure washer. A pressure washer’s GPM rating refers to the water flow during one minute of operation. The higher the PSI and GPM, the more cleaning power available and the more articles that can be cleaned.

Performance Standard

PW101, Standard for Testing and Rating Performance of Pressure Washers: Determination of Pressure and Water Flow provides for a uniform method of testing and rating the pressure and water flow of pressure washers. The standard applies to pressure washers intended for the household, farm, consumer, or commercial/industrial markets.

PWMA members and other pressure washer manufacturers test their pressure washers in accordance with PW101. By testing pressure washers to PW101, manufacturers can determine the performance of the pressure washer (PSI and GPM).

The following highlights the key testing parameters as prescribed in PW101:

  • All instrumentation must be calibrated in accordance with the National Institute of Standards & Technology (NIST) or other international measurement standards recognized by NIST.
  • All test equipment (measuring devices) must be recorded. Equipment includes: pressure measurement device, flow measurement device, rpm sensor, ammeter and voltmeter.
  • Units are tested after a break in period with production hose, gun wand, and nozzle as intended for sale. Units are broken in by running for a minimum of two (2) hours and a maximum of five (5) hours prior to test. Units are cycled on and off two times a minute (20 seconds in spray mode and 10 seconds in no-spray mode). There are more specific requirements for battery-operated units in the standard.
  • Units are tested at factory settings or the maximum performance setting(s) that can be achieved when using the pressure washer.
  • With consideration given to manufacturing tolerances of the engine or electric motor, pump assembly, nozzle, etc., performance shall be a minimum of 90% of rated psi and gpm for all units. For instance, if a company advertises a pressure washer’s performance at 1800 psi and 1.1 gpm, then the test results cannot fall under 1620 psi or 0.99 gpm.
  • Units are tested at the set pressure condition when taking pressure and flow measurements at the same time. Total stop, trapped, or spike pressure is not used when determining the ratings of the units. Consumers need to ensure that when purchasing a pressure washer that the advertised psi is not based on spike pressure. Spike pressure is experienced for a brief second and it is not usable pressure since there is no active spraying when the pressure washer reaches this spike/trap pressure.
  • Units are tested for 30 minutes of continuous operation; readings are recorded every five minutes and the average is calculated. The average value is used to establish the unit performance and conformance ratings. Pressure and water flow ratings are determined from maximum pressure and the operating flow test results average of three sample units.
  • The pressure and flow ratings are displayed on the product and packaging as a combination when tested concurrently with the production nozzle (e.g. 1800 psi, 1.1 gpm).

Third-Party Certification Program

Annually, the third party Program Administrator, Intertek, randomly selects pressure washers for testing. A program participant provides Intertek with a list of all their production models of pressure washers. Intertek then purchases the pressure washers from an outlet (e.g., internet, retailer) that sells the pressure washers. These units are tested to verify that they meet the program participants’ certified published performance ratings.

Intertek conducts the testing as prescribed in PW101. Each program participant is required to have at least two models tested; however, it could be three models (one gas unit, one electric unit, one battery-operated).  Three sample units of each model is tested so a minimum of six pressure washers are tested.

Intertek provides the program participants and the PWMA office with the test results. If the test models pass the testing performed by Intertek, the program participants can use the PWMA certification seal on their web site, products and product literature. If the tests reveal that the pressure washers do not meet the advertised performance ratings, the program participant is required to re-rate the pressure washers and change all advertisements to reflect the accurate performance ratings.

PWMA members are required to use a third-party certification program using an independent laboratory to conduct testing to evaluate performance in accordance with an industry standard. Pressure washer manufacturers whom are members of other trade associations may use self-certified products which are tested by the manufacturer using testing methods that they deem appropriate.  


There are many brands of pressure washers to choose from in the market so consumers need to be educated on pressure washer performance. Advertised PSI and GPM ratings for pressure washers can be misleading. Consumers who purchase pressure washers with a PWMA certification mark on the packaging can be assured that the pressure washer will deliver the psi and gpm that is advertised.

For information on PW101, the certification, selection guidelines, maintenance tips, visit www.pwma.org.