PIR Calculator: Get Your Foam Cannon Mix Right Every Time
Use the calculator below to work out exactly how much shampoo to add to your foam cannon. Then read on to learn how to measure your setup.
Panel Impact Ratio (PIR) tells you exactly how much shampoo concentrate is hitting the panel. Every pressure washer and foam cannon combination dilutes differently, so two detailers running the same "1:10 mix" can get completely different foam on the panel.
The calculator below does the maths for you. If you already know your output volume, plug it in. If not, scroll down for the 4 step measurement guide.
PIR Foam Cannon Calculator
The total water you measured in the bucket
1% light, 2% standard, 3-5% heavy
Don't know your output volume? Skip to the 4 step measurement guide below.
What Is Panel Impact Ratio (PIR)?
PIR is the percentage of shampoo concentrate that ends up on the panel when your foam cannon sprays.
Definition: Panel Impact Ratio (PIR) is the percentage of chemical product (shampoo or pre wash) that hits the vehicle panel when mixed with water through a foam cannon. It is calculated by dividing the amount of product in your cannon bottle by the total water output during a spray cycle.
Why it replaces dilution ratios: A "1:10 dilution" on a bottle assumes your foam cannon and pressure washer behave a certain way. They rarely do. PIR measures the actual output for YOUR setup, making it a far more reliable measure of what ends up on the panel.
How To Measure Your Foam Cannon Output
Do this once for your setup. The number you get plugs into the calculator above. Use it forever (until you change something in the chain).
Fill Your Foam Cannon With 1 Litre Of Water
Use plain water only. Set your foam cannon's metering valve to your usual working position. Attach to your pressure washer exactly how you normally run it.
Spray Into A Bucket Until Empty
Squeeze the trigger and spray into a large bucket until your cannon bottle is completely empty. Then measure how much water ended up in the bucket. This is your output volume. For most setups, 1L of bottle volume produces around 10 to 12 litres of output.
Convert To Millilitres
Multiply your output in litres by 1000 to get millilitres. This is the number you plug into the calculator at the top.
Example: 11.356 litres × 1000 = 11,356 mL output
Plug It Into The Calculator
Scroll back to the calculator, enter your output volume in mL, pick your target PIR (1% to 5%), and it tells you exactly how much shampoo concentrate to add to the bottle. Top up to your bottle volume with water and you're ready to wash.
Why PIR Matters More Than Dilution Ratios
Dilution ratios assume every setup is identical. Real world setups are not. Here is what changes the actual product reaching the panel.
Pressure Washer Flow Rate
A 9.5 LPM machine pulls more water through the cannon than a 7 LPM unit. More water means lower PIR for the same bottle mix.
Foam Cannon Model
FOAMR PRO+, MTM PF22, Maxshine cannons all have different orifice sizes and metering valves. Same bottle contents create different foam.
Metering Valve Position
Even on the same cannon, opening the metering valve halfway vs fully changes output by a wide margin. PIR locks in your usual setting.
Bottle Size
A 1L cannon, 1.5L cannon, or 2L garden hose foamer all hold different amounts. PIR scales with the bottle so you do not run out mid wash.
What PIR Percentage Should You Use?
Different jobs need different concentrations. Here are the typical PIR ranges for common detailing situations.
1% PIR
Coated cars, weekly maintenance wash, light dust only.
Example: 11L output = 110 ml shampoo
2% PIR
Most weekly washes on normal cars with light to moderate dirt.
Example: 11L output = 220 ml shampoo
3% to 5% PIR
Dirty cars, road grime, salt, mud, or after off road use.
Example: 11L output = 330 to 550 ml shampoo
Important: Always check your shampoo manufacturer's recommendations. Some highly concentrated shampoos (like Koch Chemie Magic Foam or Labocosmetica Triade) deliver excellent foam at 1% PIR. Others need 2 to 3% to perform properly. Start at the brand recommended PIR and adjust from there.
PIR For Different Foam Cannon Sizes
Bottle size changes the maths but not the principle. Here is how to calculate PIR for common foam cannon and foamer sizes.
Note: These are example output volumes. Always measure your own setup for accuracy.
Common PIR Mistakes To Avoid
These are the four most common errors that throw off your PIR and waste shampoo.
Mistake 1: Not measuring your own output
Don't assume your output is 11L. Measure it. Output varies by pressure washer, foam cannon, hose length, and metering valve position. A 5 minute measurement saves litres of wasted shampoo.
Mistake 2: Trusting the bottle dilution ratio
A label that says "1:10" assumes a specific setup the manufacturer tested with. Your setup is different. PIR accounts for your real world output, not lab conditions.
Mistake 3: Changing the cannon setting between washes
If you measured PIR with the metering valve fully open, then run a wash with it half closed, your PIR is wrong. Lock in your usual setting and stick to it. Re measure if you change.
Mistake 4: Using the same PIR for every job
A coated daily driver needs 1% PIR. A muddy 4WD needs 3 to 5%. Match PIR to the job, not the habit. Cars get cleaner faster and you save shampoo.
Foam Cannons and Shampoo
PIR only works with a quality foam cannon and a properly formulated car shampoo. Browse our range of professional foam cannons and Australian and European shampoos at Detailing Shed.
Frequently Asked Questions About PIR
What does PIR stand for in car detailing?
PIR stands for Panel Impact Ratio. It is the percentage of shampoo concentrate that actually hits the car panel when sprayed through a foam cannon, accounting for water dilution caused by your specific pressure washer and cannon setup.
Is PIR the same as dilution ratio?
No. Dilution ratio is what you mix in the bottle. PIR is what reaches the car. Because pressure washers and foam cannons pull water through differently, the same bottle dilution can produce very different results on the panel. PIR is the more accurate measure.
How do I measure my foam cannon output?
Fill the cannon bottle with 1 litre of plain water, attach to your pressure washer, and spray into a bucket until the bottle is empty. Then measure the water collected in the bucket. That's your output volume.
What's a good PIR for a weekly car wash?
2% PIR is the standard target for most weekly washes on cars with light to moderate dirt. Coated cars on maintenance washes can drop to 1%, while heavy pre wash for dirty 4WDs typically needs 3% to 5%. Adjust based on the shampoo manufacturer's recommendations.
Do I need to recalculate PIR if I change my pressure washer?
Yes. A different pressure washer with different flow rate will pull water through the cannon at a different rate, changing your output volume. Re measure whenever you change pressure washer, foam cannon, or hose length.
Does PIR work for garden hose foamers too?
Yes, but the principle is slightly different. Garden hose foamers don't dilute the bottle contents like a pressure washer foam cannon does. The PIR is closer to the bottle dilution itself. Still measure your output for accuracy.
Can I use PIR for wheel cleaners or pre wash chemicals?
Absolutely. PIR works for any product applied through a foam cannon or sprayer. Wheel cleaners and iron removers typically run higher PIR (3 to 5%) for effective cleaning. Always follow chemical manufacturer's guidelines.
What if my foam cannon doesn't have a metering valve?
PIR still works. Without a metering valve, your output rate is fixed by the cannon design. Measure once and you have your number forever. If your cannon has multiple nozzle settings, measure for each setting you regularly use.
Whether you're choosing your first foam cannon, matching shampoo to your pressure washer, or troubleshooting weak foam, we can help you dial in the right PIR for your setup. Call us or email Detailing Shed and we'll talk you through it.