How to Size an Air Compressor for Your Sydney Workshop: CFM, PSI & Tank Sizing Guide

How to Size an Air Compressor for Your Sydney Workshop: CFM, PSI & Tank Sizing Guide

TL;DR: To size an air compressor, add up the CFM of every tool that runs at the same time, add 25 to 30 per cent headroom, then choose a machine that delivers that flow at a pressure about 20 to 30 PSI above your highest tool rating. Match the receiver tank to how lumpy your demand is, and confirm your power supply before you buy.

Most undersized compressors are not faulty. They were simply chosen by horsepower or price instead of by the air the workshop actually uses. If you have ever watched a sander slow down mid-job or heard a compressor run flat out all day, you already know what a sizing mistake feels like.

This guide shows how to size an air compressor for a Sydney workshop in five steps, with a worked example, so you can walk into a conversation about air compressors in Sydney knowing your numbers.

What CFM, PSI and tank size actually mean

CFM (cubic feet per minute) measures airflow. It is the single most important number when sizing an air compressor, because it tells you how many tools you can run at once. One CFM equals about 0.47 litres per second, which is how many Australian data sheets list it.

PSI (pounds per square inch) measures pressure. Most workshop tools are rated at around 90 PSI, which is about 6.2 bar. Pressure sets how hard the air pushes. Flow sets how long it can keep pushing.

Tank size (the air receiver) stores compressed air so the compressor does not have to start and stop every time you pull a trigger. A bigger tank smooths out demand. It does not create more air.

A quotable rule worth remembering is that CFM decides whether your tools keep working, PSI decides whether they work properly, and the tank decides how often the compressor cycles.

Step 1. List every air tool and its CFM rating

Walk the workshop and write down each air tool, with the CFM figure from its data plate or manual. The figure is usually quoted at 90 PSI. These are typical ranges, so always trust the plate on your own tool:

• Impact wrench (half inch): roughly 4 to 5 CFM

• Air ratchet or die grinder: roughly 4 to 6 CFM

• Orbital or DA sander: roughly 8 to 12 CFM

• Spray gun: roughly 8 to 15 CFM

• Blasting equipment: often 20 CFM or far more, depending on nozzle size

Blasting and sanding are the usual culprits when a workshop outgrows its compressor.

Step 2. Work out what runs at the same time

Adding every tool together overstates your needs, because few workshops run everything at once. Instead, identify your realistic peak. That means the tools that run together, plus a fraction of the intermittent ones.

Impact wrenches and ratchets fire in short bursts, so count them at about 25 to 30 per cent of their rated CFM. Continuous tools like sanders and spray guns count at full value.

Worked example. A panel and paint shop in Alexandria runs a spray gun (10 CFM) and a DA sander (9 CFM) together, with an impact wrench (5 CFM) used on and off nearby.

1. Spray gun at 100 per cent: 10 CFM

2. DA sander at 100 per cent: 9 CFM

3. Impact wrench at about 30 per cent: 1.5 CFM

4. Realistic peak demand: about 20.5 CFM

Step 3. Add headroom for leaks, wear and growth

Add 25 to 30 per cent to your peak figure. This covers small leaks, filter pressure drop, tool wear and the new tool you will inevitably buy next year. Leaks alone can waste a surprising share of output in an unmaintained system, which is one reason regular servicing pays for itself.

In the example, 20.5 CFM plus roughly 30 per cent gives about 27 CFM. That is your target delivery, ideally quoted as free air delivery (FAD) rather than a displacement figure. FAD is what the compressor actually delivers, and the two numbers can differ considerably.

Step 4. Choose your operating pressure

Find the highest pressure rating among your tools, then add 20 to 30 PSI. That buffer covers pressure lost through hoses, fittings, filters and dryers between the compressor and the tool.

If your tools need 90 PSI, a compressor set to run in the range of 100 to 125 PSI (about 7 to 8.6 bar) will serve you well. Buying a machine with a much higher rating than you need rarely helps, because it costs more to run. Buying one that barely reaches your tool pressure leaves you with weak performance at the end of a long hose.

Step 5. Match the tank to your demand pattern

A common installer rule of thumb is around 4 litres of receiver volume for every 1 CFM of compressor output. For 27 CFM, that points to roughly 110 litres as a starting point. Choose a larger receiver if your demand is spiky, for example a shop where several tools fire together then sit idle, or if you want fewer start-stop cycles to protect the motor.

The exact figure depends on the compressor’s control type and your demand profile, so treat this as a starting estimate and have a technician confirm it. Remember that air receivers are pressure vessels. In New South Wales they need to be registered where required and inspected on schedule, and the SafeWork NSW guidance on pressure equipment is the right place to confirm current obligations for your site.

Piston vs rotary screw for a Sydney workshop

The choice between piston and rotary screw is the other big sizing decision, and it affects how you read your CFM figure.

Piston compressors suit smaller workshops with intermittent demand. They are generally cheaper upfront, but they are not built to run continuously. Most are designed for a duty cycle well below 100 per cent, so a piston unit sized exactly to your CFM may struggle if your tools run all day.

Rotary screw compressors are built for continuous duty. They deliver steady flow, run quieter, and usually suit workshops running sanders, spray equipment or multiple stations. Variable speed drive models match output to demand and can cut energy use where demand fluctuates through the day.

All Air Compressors supplies both. Their products for sale range covers belt-driven oil-lubricated screw compressors from 2 to 11 kW, direct-drive screw models up to 250 kW, oil-free screw machines, and piston compressors from 2 to 30 kW in single-stage and two-stage configurations. As a rough guide, a screw compressor tends to deliver somewhere in the region of 3 to 4 CFM per kW, though individual models vary, so always check the data sheet.

Factors that catch Sydney workshops out

Sizing on paper is only half the job. Local conditions change what a compressor delivers in practice.

• Heat. A compressor working in a hot, poorly ventilated shed in Western Sydney during summer will deliver less air and run hotter than its rating suggests. Allow for ventilation, or size up.

• Humidity and coastal air. Moist air produces more condensation in the system. Workshops near the harbour, from Pyrmont to Balmain, should plan for an air dryer and proper drain valves to protect tools and paint finishes.

• Noise. Inner-city workshops in places like Surry Hills, Chippendale and Ultimo often sit close to neighbours. A silenced or encapsulated unit can keep you on good terms with the street.

• Power supply. Smaller compressors run on single-phase power, but larger machines usually need three-phase. Check your switchboard before choosing, because an electrician’s upgrade can add cost and delay.

• Floor space and access. Measure the doorway as well as the room. Tall receivers and larger frames have to get in before they can run.

Not sure your numbers add up? Ask the team before you buy

Sizing mistakes are expensive in both directions. An undersized compressor runs flat out and wears early, while an oversized one wastes energy and capital. If you would like a second opinion, you can contact All Air Compressors with your tool list and we can check your CFM, pressure and tank figures against your actual workshop. Ask for a workshop sizing check before the busy pre-summer period, when lead times and demand for service tend to tighten.

What if you only need air for a short project?

If your demand is temporary, such as a refit, a seasonal rush or a trial run on a new process, buying outright may not be the best answer. Compressor hire lets you test your real CFM demand on a rented machine first, then buy the right-sized unit with confidence.

Keep your compressor sized correctly over time

A compressor that was correctly sized on day one can drift out of spec. Filters clog, valves wear and leaks creep in, all of which reduce the air reaching your tools. A tailored preventative maintenance plan keeps delivery close to rated output, and a proper compressor servicing and repairs schedule is the cheapest way to avoid an unplanned shutdown. For more practical guidance, browse the useful information hub.

Sizing an air compressor, answered quickly

How many CFM do I need for my workshop?
Add up the CFM of every tool that runs at the same time, count intermittent tools at about 30 per cent, then add 25 to 30 per cent headroom. That total is your target free air delivery.

What PSI should my compressor run at?
Most workshop tools need about 90 PSI, so a compressor set to around 100 to 125 PSI usually covers pressure lost through hoses and fittings.

What size air receiver tank do I need?
A common starting point is roughly 4 litres of tank for every 1 CFM of output, with a larger tank for spiky demand. A technician should confirm the figure for your control type.

Should I choose a piston or rotary screw compressor?
Choose piston for light, intermittent use. Choose rotary screw for continuous duty, multiple stations or spray and sanding work.

Can I rent a compressor before I buy one?
Yes. Hiring a unit lets you measure your real demand before committing to a purchase.

Get your workshop sized properly

If you run a workshop anywhere across Sydney and want an air compressor matched to your tools, speak to the team at All Air Compressors. Send through your tool list using the online contact form and ask for a workshop compressor sizing check, so you buy the right machine the first time.