How to Check the GPM of Your Pressure Washer
- Trudi Weickum
- Jul 19
- 3 min read
When it comes to pressure washing or soft washing, understanding your equipment is everything—and one of the most important specs you need to know is your GPM (Gallons Per Minute).
Why? Because GPM determines your flow, and your flow determines how efficiently you can rinse, apply chemicals, and clean large surfaces. Whether you're running a single wand, soft wash setup, or dialing in your dual-man trailer—knowing your true GPM helps you work smarter, not harder.
Let’s break down two simple methods to test your GPM from the field—without needing lab-grade equipment.
Method 1: Using a Bucket and Scale
This method is great if you don’t have a graduated container but do have a reliable scale. It’s a little old-school—but it works.
🔧 What You’ll Need:
A 5-gallon bucket.
A stopwatch or timer. (your phone works fine)
A scale that can weigh. the water-filled bucket
💧 Step-by-Step:
Prep Your System
Fire up your pressure washer and set your nozzle to a small angle (around 15°) for consistent flow.
Fill the Bucket
Place the nozzle securely in the bucket and run water for exactly one minute.
Weigh the Water
Weigh the bucket and subtract the weight of the empty bucket to get the weight of just the water.
Do the Math
Water weighs about 8.34 lbs per gallon, so take your total weight and divide it by 8.34. That gives you total gallons collected in one minute.
Example:41.7 lbs ÷ 8.34 = 5 gallons→ GPM = 5
Method 2: Using a Calibrated Measuring Container
This is the faster and more direct method if you have a bucket with gallon markings or a graduated cylinder on hand.
🔧 What You’ll Need:
A marked container. (like a graduated bucket or tank)
A stopwatch.
💧 Step-by-Step:
Prep Your System
Same as above—run your pressure washer with a consistent nozzle setup.
Collect Water
Run water into your container for a fixed time (usually one minute).
Measure Volume
Read the number of gallons collected directly from the markings.
Calculate GPM
Divide the gallons collected by the minutes you ran it for.
Example:5 gallons in 1 minute = 5 GPM
⚠️ Things to Keep in Mind
Nozzle Type Matters:
Different nozzles restrict or open up your flow. Always note which nozzle you used when testing.
Pressure Isn’t the Whole Story:
High PSI doesn’t mean better cleaning on its own—GPM is what helps you rinse fast, apply soaps properly, and cover more area.
Accuracy Counts:
Use a reliable scale or properly marked container. Eyeballing it won’t help when you’re sizing tanks, batch mix systems, or planning jobs.
Why This Matters for Contractors
Knowing your GPM gives you:
Confidence in your setup.
Smarter chemical mix ratios.
Faster rinse and clean times.
The ability to scale. (dual-gun or soft wash add-ons)
Accurate trailer builds and plumbing designs.
If you're heading into commercial work, building out a custom rig, or just want to maximize efficiency—GPM is a number you need to know.
Final Thought
Your equipment is your business partner. If you don’t know how it's performing, you’re flying blind. Take a few minutes, run the test, and dial it in.
Because the pros who know their flow… win more jobs, rinse faster, and scale further.
Want to Learn More?
If this kind of hands-on knowledge fires you up—you need to be at the Panhandle Power Wash Expo.
🧠 Get Trained by the Pros
Meet industry leaders, manufacturers, and real-world pros who are ready to share the exact systems and tools they use every day.
🛠️ Live Demos & Equipment Training
See the latest gear in action and learn how to get the most out of your setup—whether you're new to the game or scaling up your crew.
🤝 Build Your Network
Connect with contractors, vendors, and manufacturers who actually get it. No fluff. Just real conversations and real growth.
📍Join us at the Expo
Come shake hands, sit in on classes, and leave with actionable knowledge you can use the next day on the job site.
By Trudi Weickum | Industry Educator | Panhandle Pressure Washing Expo
Comments