Free detailing tool
Foam Cannon PIR Calculator
PIR, or panel impact ratio, is how strong your foam actually is when it hits the paint. A foam cannon mixes the bottle with pressure-washer water, so a 1:10 bottle can land as 1:100 or weaker. Do one bucket test with plain water, then this calculator tells you how much soap or pre-wash to put in the bottle for the PIR you want.
Step 1: Bucket test your cannon
Fill the bottle with plain water, set the cannon the way you normally use it, and spray it all into a bucket. Measure what you collected. A kitchen scale works: 1 gram of water is 1 ml.
Enter what you collected to continue.
Step 2: Mix the bottle
Finish step 1 and enter a target to see the mix.
How PIR works
A foam cannon does not spray what is in the bottle. It draws a small stream from the bottle into the pressure washer's water, so a full bottle turns into many times its volume of foam. The bucket test measures that number for your exact cannon, dial setting and pressure washer.
Once you know the output, the chemical you need is simply the output times the PIR. A 1 liter bottle that lays down 12 liters, at 1% PIR, needs 12,000 × 0.01 = 120 ml of chemical. Top it up with water to fill the bottle.
- Set up the cannon. Set the foam cannon dial and fan to your normal settings, on the pressure washer you use.
- Spray plain water. Fill the bottle with plain water only and spray it all into a large bucket.
- Measure the output. Weigh or measure the water collected. 1 gram is 1 ml. Enter it with your bottle size.
- Mix the bottle. Enter the PIR or panel ratio you want. The calculator shows the chemical and water for the bottle.
Common PIR starting points
General starting points. Your product label comes first.
| PIR | At the paint | Typical use |
|---|---|---|
| 0.25% | about 1:399 | Maintenance wash, very light dirt |
| 0.5% | about 1:199 | Foam pre-wash, contact wash |
| 1% | about 1:99 | Decontamination pre-wash, iron fallout |
| 2% | about 1:49 | Heavily soiled vehicles, engine bays |
| 3% | about 1:32 | Extreme contamination, longer dwell foam |
| 4% | about 1:24 | Maximum strength, spot treatment |
Mixing a spray bottle or bucket instead? Use the dilution ratio calculator.
Frequently Asked Questions
PIR is the strength of the chemical when it reaches the paint, after the foam cannon has mixed the bottle with water from the pressure washer. It is written as a percent or a ratio. A 1% PIR is about 1:99 at the panel.
It depends on how much water your cannon and pressure washer push through, which is why you bucket test first. For example, if a 1 liter bottle comes out as 12 liters and you want 1% PIR, you need 120 ml of soap topped up to 1 liter with water.
Fill the bottle with plain water, set the cannon's knob and fan the way you normally use them, and spray the whole bottle into a large bucket. Weigh or measure what you collected. One gram of water is one milliliter, so a kitchen scale works well.
The cannon pulls a little of the bottle into a lot of pressure-washer water. Most setups lay down 8 to 20 times the bottle volume, so the foam on the paint is that many times weaker than the bottle.
Yes. The dial changes how much of the bottle the cannon draws, which changes the output and the PIR. Bucket test with the dial where you actually use it, and test again if you move it or change pressure washers.
Many snow foams and pre-washes are run around 0.5% to 1% PIR, with stronger mixes for heavy dirt. The product label is the final word, and some labels give a PIR directly. The reference table on this page lists common starting points.
More tools
- Dilution Ratio Calculator
Chemical and water for any ratio and bottle size, a ratio chart, and pre-mix adjustments.
- Detailing guides
Plain answers on coatings, correction, headlights and care in the Arizona sun.
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