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Pressure washer nozzle size calculator for car detailing

Calculate a pressure-washer nozzle-number reference from operating flow and target pressure, then screen an exact spray tip or foam cannon using current manufacturer evidence.

Calculate a nozzle-number reference from the exact machine flow and target pressure. Then screen one spray tip or foam-cannon candidate against its current chart, ratings and connection evidence.

Machine requirement

The calculation uses US gpm and psi internally because the published nozzle-number formula is expressed in those units.
Spray tips and foam cannons need different evidence after the hydraulic reference is calculated.
Use the current exact-model manual or manufacturer performance data, not a retailer headline.
L/min
Enter the operating flow used by the manufacturer chart, not an assumed tap or pump-supply value.
bar
This is the pressure target used in the reference calculation, not automatically a safe surface pressure.
bar
Use the lowest applicable maximum across every component in the pressure path.

Exact candidate screen

Record the current exact-model specification or manual for the tip, holder or foam cannon.
Confirm how the manufacturer maps machine flow and pressure to this nozzle or orifice.
Confirm gun, lance, holder, couplers, adapters, threads and every applicable pressure rating.
No.
Enter the nozzle number from the exact manufacturer evidence—not only an orifice diameter in millimetres.
bar
Use the candidate’s published maximum; it must be reconciled with the complete pressure path.
Nozzle number does not select spray angle, distance or a safe procedure for a vehicle surface.

Nozzle direction

Record the machine requirement first

Still needed: the exact machine flow and pressure evidence and the rated operating flow and a target operating pressure and the complete-line maximum working pressure

Nozzle number is calculated from operating flow and target pressure. A headline maximum-pressure claim cannot replace the exact machine evidence.

Formula reference—

Nozzle number—not millimetres, spray angle or product approval

Rated machine flowConfirm machine
Target operating pressureConfirm machine
Candidate nozzle numberAdd candidate
Candidate formula estimateAdd candidate
Difference from targetAdd candidate
Candidate evidenceStill incomplete
The formula No. = US gpm × √(4000 ÷ psi) is a chart reference. A result does not choose spray angle, approve a surface procedure, certify a connector or override the exact manufacturer instructions.
  1. 01

    Record the exact machine operating flow, target pressure and complete-line maximum working pressure from current evidence.

  2. 02

    Nozzle number and spray angle are separate choices. Confirm the exact angle, working distance and surface procedure before applying pressure to vehicle paint, trim, tyres or sensitive areas.

  3. 03

    Rate the complete pressure path: machine outlet, hose, reel, gun, lance, couplers, adapters, nozzle holder and attachment. The lowest applicable limit controls.

  4. 04

    Use the exact manufacturer selection chart where it differs from this hydraulic reference. Do not infer compatibility from thread appearance, colour coding or a retailer title.

  5. 05

    Confirm the spray tip material, nozzle number, connector, retained condition and cleaning procedure; replace damaged or enlarged tips using the exact instructions.

  6. 06

    Stop if the machine pulses, cycles unexpectedly, leaks, loses stable pressure or behaves differently after a nozzle change. Isolate it and follow the exact troubleshooting instructions.

Return to the machine selector Check inlet delivery separately Check the complete hose path
Affiliate disclosure: As an Amazon Associate I earn from qualifying purchases. The price is unchanged for you. Retailer results are not manufacturer charts, pressure ratings, surface procedures or compatibility approvals. Outside the UK, use equivalent local retailers and the rules that apply where the equipment is used.

One formula, several separate decisions

Nozzle number is only the chart starting point.

The published reference connects flow, pressure and nozzle number. It does not choose the spray angle, chemical attachment, working distance, connector or safe process for a vehicle surface.

01Record machine evidence

Operating flow, target pressure and the complete-line maximum rating.

02Calculate the reference

Use the result to find the neighbouring sizes in the exact chart.

03Screen one candidate

Rating, chart selection, connectors and attachment-specific evidence.

04Verify the process

Spray angle, surface distance, unloader behaviour and current instructions.

Build the complete path

The lowest applicable limit controls.

The machine outlet, hose, reel, gun, lance, couplers, adapters, holder and attachment form one pressure path. A nozzle result cannot raise the working-pressure rating of another component or correct an incompatible connection.

Choose the machine class with the pressure washer selector, verify inlet delivery in the tank-to-washer checker, then size the working hose path with the hose reel selector.

Current-source boundary

Use the formula to find the chart—not to replace it.

These primary references show the nozzle-number equation, the relationship between flow and pressure, attachment-specific selection evidence and pressure-washer safety boundaries. Product references are examples, not endorsements.

General PumpOfficial nozzle chart and flow-pressure formulaGeneral PumpFAQ on flow, nozzle orifice and pressure behaviourMTM HydroOfficial foam-cannon service manuals and selection chartsMTM HydroExact orifice example with machine-matching warningHSEElectrical pressure-washer workplace safety guidance
Source review: 13 September 2026. Recheck the current exact-model instructions, charts and rules before purchase or use.

Questions before checkout

Pressure washer nozzle-size questions

How do I calculate pressure washer nozzle size?

A commonly published hydraulic reference is nozzle number equals US gallons per minute multiplied by the square root of 4000 divided by pressure in psi. Use operating flow and the intended pressure from the exact machine evidence, then compare the neighbouring sizes in the manufacturer chart.

What does a pressure washer nozzle number mean?

It is a rated-orifice reference used with flow and pressure charts. It is not a millimetre diameter, spray angle, connector size, colour code, surface-safety approval or complete product specification.

Does a smaller nozzle number create more pressure?

For a fixed flow, the reference equation estimates higher pressure through a smaller nozzle number and lower pressure through a larger one. The real machine, unloader, wear, restrictions and exact manufacturer instructions still control the usable arrangement.

Is a foam cannon orifice the same as a spray nozzle number?

Do not assume they are interchangeable labels. A foam-cannon maker may publish both an orifice diameter and a nozzle-number equivalent, alongside a machine flow and pressure range. Record the exact terminology and fitted part for that model.

Should every low-flow pressure washer use a 1.1 mm foam-cannon orifice?

No. A frequently mentioned orifice size is not a universal recommendation. Use the exact foam-cannon chart, pressure-washer instructions, flow and pressure range, connector evidence and any unloader restrictions.

Does nozzle size choose the spray angle for detailing?

No. Nozzle number and spray angle are separate decisions. Confirm the surface procedure, angle, working distance and exclusions before applying pressure to paint, trim, tyres, seals or sensitive components.

Why does a pressure washer pulse after changing a nozzle or foam cannon?

Pulsing can have several machine- and system-specific causes. Stop, isolate the equipment and follow the exact manufacturer troubleshooting instructions rather than continuing with a guessed orifice change.