Thin, watery snow foam is usually a mismatch between the pressure washer and the small brass orifice inside the foam cannon. Enter two figures from your machine and this calculator shows which orifice size suits it, and how much pressure each size leaves you with.

Which orifice for which machine

The orifice is a drilled brass jet a little over a millimetre wide. All the water from your machine has to pass through it. A smaller hole makes the water leave faster, which pulls more product up from the bottle and whips more air into it. That is what makes foam thick.

Too large for your flow and the pressure drops away. The cannon draws less product and the foam comes out thin and wet.
Too small for your flow and the pump is pushed past the pressure it was built for. The machine pulses, cuts in and out, or trips.
Matched and the machine runs at close to its rated pressure with the cannon on. That is the size to use.

Orifice chart for common machine sizes

Estimated pressure at the cannon for each orifice. Tight means a little small for the flow. The last column is the size to fit.

Rated pressure	Flow	1.1 mm	1.25 mm	1.4 mm	1.5 mm	Fit
100 bar	330 L/h	65 bar	48 bar	29 bar	23 bar	1.1 mm
110 bar	360 L/h	77 bar	57 bar	34 bar	28 bar	1.1 mm
120 bar	400 L/h	95 bar	70 bar	42 bar	34 bar	1.1 mm
130 bar	420 L/h	105 bar	77 bar	47 bar	38 bar	1.1 mm
140 bar	480 L/h	137 bar	101 bar	61 bar	49 bar	1.1 mm
150 bar	500 L/h	149 bar	109 bar	66 bar	53 bar	1.1 mm
160 bar	550 L/h	160 bar	132 bar	80 bar	65 bar	1.1 mm
180 bar	600 L/h	Tight	157 bar	95 bar	77 bar	1.25 mm
200 bar	720 L/h	Too small	200 bar	137 bar	111 bar	1.25 mm
250 bar	900 L/h	Too small	Too small	214 bar	173 bar	1.4 mm

Typical home electric pressure washers sit in the top half of this chart, which is why a 1.1 mm orifice suits them. Our Snow Foam Cannon is fitted with a 1.1 mm orifice and is rated up to 160 bar.

How the calculator works

Pressure washer nozzles are sold by a size number. It comes from one formula that the whole industry uses:

Nozzle size = flow in US gallons a minute × the square root of (4000 / pressure in PSI)

The calculator works out the nozzle size your machine is built around from its rated pressure and flow.
Each foam cannon orifice has a nozzle size of its own. A 1.1 mm orifice is sold as a size 3.0, 1.25 mm as a 3.5, 1.4 mm as a 4.5 and 1.5 mm as a 5.0.
If the orifice is larger than the machine's own size, pressure falls with the square of the difference. A 1.25 mm orifice on a machine built around a size 3.0 nozzle leaves about 73% of full pressure.
If the orifice is a little smaller than the machine's own size, the machine sheds the extra flow and stays at full pressure. Up to about 7% smaller counts as a match. Up to about 16% smaller is marked tight. Beyond that it is marked too small.

It does not predict how thick your foam will be. That also depends on the product, the mix in the bottle, the mesh inside the cannon and your water. What it does tell you is whether the orifice is holding your machine back.

What dilution actually reaches the car

The ratio you mix in the bottle is not the ratio that lands on the paint. The cannon blends a thin stream of that mix into all the water coming from the machine. You can measure it. Fill the bottle, time how long it takes to empty with the trigger held, and enter the figures here. It uses the flow you entered above.

Turning the top dial towards maximum empties the bottle faster and makes the foam richer. Turning it down stretches the bottle and thins the foam. Timing the bottle at each end of the dial shows you the range your cannon covers.

Why is my snow foam watery?

Work down this list in order. The first three account for most cases.

The orifice is too large for your machine. Check it with the calculator above. Many cannons are sold with a 1.25 mm orifice, which is too large for a lot of home machines.
The top dial is turned down. It controls how much mix is drawn from the bottle. Turn it fully towards maximum and work back.
The mix in the bottle is too weak. Measure it. For No.02 Snow Foam that is about 65 ml topped up to 1 litre (1:15), or about 90 ml for the Extreme formula (1:10). Our dilution ratio calculator covers other sizes.
The mesh filter is clogged. Inside the cannon is a small pad of stainless steel mesh that turns the mix into foam. Dried product blocks it. Soak it in warm water or replace it.
The orifice is partly blocked. Grit or limescale in a hole this small cuts the draw. Run clean water through the cannon after every use.
The pickup tube is loose or split. If the cannon sucks air, it cannot draw mix.
The fan is set too wide. A narrower fan gives a denser foam.
Your water is very hard. Hard water makes every detergent foam less. A slightly richer mix, within the label ratio, helps.
The product is not a snow foam. A bucket shampoo is made to be slick, not to cling.

Thick foam is not the goal on its own. A foam that runs slowly down the panel carries more dirt away than one that sits like shaving cream. Our foam cannon guide covers the full routine.

Common questions

Is a 1.1 mm or 1.25 mm orifice better for a foam cannon?

It depends on the flow of your pressure washer. A 1.1 mm orifice suits most electric machines, which deliver roughly 5 to 9 litres a minute. A 1.25 mm orifice suits machines with more flow for their pressure. Fitting a 1.25 mm orifice to a low flow machine drops the pressure and thins the foam.

Can a 1.1 mm orifice damage my pressure washer?

Not if it is matched to the machine. An orifice that is too small for the flow pushes the pump to its limit, and the machine will pulse or cut out. If that happens, stop and fit the next size up.

How do I convert bar and litres an hour to PSI and GPM?

Multiply bar by 14.5 to get PSI. Divide litres an hour by 60 to get litres a minute, then divide by 3.785 to get US gallons a minute. A 130 bar, 420 litres an hour machine is about 1885 PSI and 1.85 GPM.

What orifice size is in the SoapX foam cannon?

1.1 mm, in a solid brass body rated up to 160 bar. It suits most home pressure washers.

How much snow foam goes in a 1 litre foam cannon bottle?

For SoapX snow foam in the Summer, Winter or Delicate formula, about 65 ml topped up to the 1 litre line with water, which is 1:15. The Extreme formula is 1:10, about 90 ml. Add the water first so the bottle does not foam over.

Where the figures come from

Nozzle size formula: Dultmeier nozzle size calculator.
Nozzle sizes and orifice diameters: Cat Pumps nozzle selection chart.
Foam cannon orifice sizes: MTM Hydro orifice listings.

You are welcome to link to this calculator or quote the chart. Spotted a machine it gets wrong? Email hello@soapx.co.uk and we will look at it.

Foam Cannon Orifice Calculator