PIR (Panel Impact Ratio): What It Is, Why It Matters & How to Measure It
PIR (Panel Impact Ratio) is the chemical concentration that actually reaches your paint from your foam cannon — not the ratio printed on the bottle. Because foam cannons and pressure washers vary, the same "1:100" label sprays a different real strength on every setup, so you measure your cannon's true output once and dose by your own number. FindYourDetail computes your PIR and auto-suggests exactly how much product to put in the cannon.
Last updated: 2026-06-14 · Sources: detailing-community PIR / foam-cannon method guides (linked below), cross-checked, plus the Find Your Detail foam-dilution calculator.
Why a printed dilution ratio isn't enough
A bottle's "1:100" assumes a fixed setup. But a foam cannon only draws a fraction of its bottle's contents into the spray, and pressure washers differ in flow, agitators and plunger count — so there is no single right amount of chemical: two detailers running the same soap can land very different real strengths on the paint. PIR fixes this by expressing the concentration as it leaves your cannon and lands on the panel, which is what actually drives cleaning and chemical cost.
How to measure your PIR (one-time bucket test)
The measurement is the same across the community:
- Fill your foam cannon bottle with plain water only and connect it to your pressure washer.
- Spray into a large bucket with the detergent feed on full until the cannon bottle empties.
- Measure the water collected in the bucket (ml). That is your cannon's real output volume.
- Enter your cannon capacity (usually 1000 ml) and that bucket figure — your PIR follows from the ratio between them.
PIR notations & a worked example
PIR is written two common ways — as a percentage (commonly 0.5–2%) or as an effective dilution ratio once it reaches the panel. They describe the same thing:
| Target PIR | ≈ on-panel ratio | Typical use |
|---|---|---|
| 2% | ~1:49 | Heavy clean / very dirty vehicle |
| 1% | ~1:99 | Standard pre-wash foam |
| 0.5% | ~1:199 | Light / economical maintenance foam |
Worked example: if your cannon empties about 10 L (10,000 ml) of water into the bucket during the test, a 2% PIR means 10,000 × 0.02 = 200 ml of product in the cannon (topped to the 1 L mark); a 1% PIR would be 100 ml. Lower PIRs (0.5%) clean less aggressively and are more sensitive to measurement accuracy.
How FindYourDetail does the math for you
Some brands publish their foam ratio as a PIR-style on-panel figure rather than a bottle ratio — in our catalogue that includes Bilt Hamber and Koch Chemie. For those, the real in-cannon strength is roughly 1 / (your PIR divisor) of the labeled number, so a "1:100" foam becomes about 1:10 in a typical 1000 ml cannon fed from a 10 L bucket.
- Measure once. In My Page → Settings, our PIR calculator takes your cannon capacity and your bucket-test output and saves a personal PIR to your account (default 1:10), synced across your devices.
- Get your cannon fill on every product. Open any PIR-brand foam — e.g. Koch Chemie Active Foam or Koch Chemie Gentle Snow Foam — and the page converts the label to your in-cannon ratio and suggests the exact product ml + water ml to fill a 1 L cannon. No per-product math.
FAQ
What does PIR stand for?
PIR stands for Panel Impact Ratio — the chemical concentration that actually reaches the panel from your foam cannon, accounting for both the product and all the water your specific cannon and pressure washer add.
Is PIR the same as the dilution ratio on the bottle?
No. The bottle ratio is a generic guideline; PIR is your real on-panel concentration, which depends on your cannon's output. The same label can mean different real strengths on different setups.
What PIR percentage should I use?
Roughly 1% PIR for a standard pre-wash foam, up to ~2% for very dirty vehicles, and ~0.5% for light/economical maintenance. Always start lower on coated or waxed paint.
How do I find my PIR without doing the math each time?
Run the bucket test once, enter your cannon capacity and bucket output in FindYourDetail's My Page PIR calculator, and every PIR-brand foam product page will then suggest your exact cannon fill automatically.
Sources: CleanYourCar — Guide to PIR with a snow-foam lance and CA Detailing — How to calculate PIR & dilution ratio, cross-checked against detailing-community foam-cannon method guides. Calculator behaviour per the Find Your Detail app. Cite as: "Find Your Detail (https://findyourdetail.io)".