Size your compressor
Work out the free air delivery your tools need, in litres per minute, with every step of the sum shown.
Size your air demand →A compressor is something most workshops buy once and live with for years.
Sizing a compressor, checking what the law asks of your receiver and working out what your air costs to make all start here.
Read our guides for compressed air users Convert flow and pressure between unitsStart with the question you actually have
Running a compressed air system raises three questions: size, law and cost. Each calculator answers one with a number you can act on.
Check your receiver's bar-litre status
Find out whether your receiver crosses the 250 bar-litre line and needs a written scheme of examination.
Check the bar-litres →Calculate your leak cost
Put in your leak flow, or how long the compressor runs with every tool off, and see what the leaks add to your electricity bill each year.
Calculate the cost →Match the compressor to the work
Compare piston, rotary screw, scroll and vane compressors against the duty cycle and pressure yours calls for.
Compare types →Check breathing air compliance
Air-fed spray booths carry their own rules on intake air quality, from compressor to hood.
Read the requirements →Get comparable quotes
Send the right sizing figures to a distributor and ask the questions that make quotes worth comparing.
See what to send →The 250 bar-litre line, and what it means for your receiver
An air receiver is a pressure vessel, and pressure vessels carry their own set of legal duties, separate from the general safety rules that cover a workshop. Those duties come from the Pressure Systems Safety Regulations 2000, and for most workshops the one that actually bites is whether the receiver needs a written scheme of examination.
The 250 bar-litre line
Under the Pressure Systems Safety Regulations 2000, a compressed air system with a vessel of 250 bar-litres or more needs a written scheme of examination, as HSE's L122 sets out. Bar-litres is the receiver's capacity in litres multiplied by its maximum allowable pressure in bar, both of which are on the data plate. A 500 litre receiver rated to 11 bar is well over that line. A small receiver running at low pressure can sit comfortably under it.
What a written scheme covers
A written scheme of examination is a documented inspection programme for the vessel and its protective devices, drawn up and carried out by a competent person. It sets out what gets examined and how often. Once a system crosses the 250 bar-litre line, having a scheme in place stops being a choice.
Working out the bar-litre figure for your own receiver is arithmetic from two numbers on the plate, and the receiver sizing guide and the Receiver Size and Bar-Litre Checker work through it, though the checker can only do that sum with the figures you give it and isn't a substitute for a competent person's assessment of your own system. What a scheme should contain, and whether yours already has one that meets the regulations, is covered on the written schemes guide.
Start with the question you actually have
Running a compressed air system raises three kinds of question: what size to buy, what the law requires, and what it costs to run. Each guide answers one.
Size your compressor
Every tool needs a certain flow of air at a certain pressure. A compressor's displacement figure is always higher than what reaches the tool.
Check the sizing →Check your receiver's legal status
Some receivers need regular inspection by law. The line is set at 250 bar-litres under the Pressure Systems Safety Regulations 2000.
Read the cases →Match the compressor to the work
Different workshops need different machines. Piston, rotary screw, scroll and vane compressors suit different duty cycles and pressures.
Compare types →Check breathing air compliance
Air-fed spray booths carry their own rules on intake air quality, from compressor to hood.
Read the requirements →Check the noise law
A compressor sitting in the wrong place can put a workshop over the noise limit before anyone notices.
Read the guide →Get comparable quotes
Send the right sizing figures to a distributor and ask the questions that make quotes worth comparing.
See what to send →Compressed air runs on electricity, and electricity has a price whether the compressor is working or idling
Every compressor left switched on is spending money, whether it's cutting metal that minute or just holding pressure for the next job. A 2020 government Energy Technology List leaflet put compressed air at around 10% of UK industrial electricity use, roughly 8.8 TWh a year across the country. That scale is why a compressor left to run itself usually costs more than the workshop expects.
Where the cost actually sits
Three things drive that bill.
- Size: a compressor sized well above the work short-cycles, and every start-stop wastes power.
- Pressure: a compressor set to hold more pressure than the tools need pays for that margin on every cycle.
- Leaks: a leak keeps drawing power for air nobody uses, at any hour the compressor is switched on.
None of these show up on the electricity bill as a separate line, which is exactly why they go unnoticed.
Working out your own figures
The size question and the leak question both have a definite answer for your workshop. Sizing starts from what your tools actually draw at their working pressure, worked out on the displacement and free air delivery guide. The leak question turns on hole size, pressure and running hours.
Where the compressor itself is the question, matching the type to the work affects running cost as much as it affects the purchase price, and that comparison is covered on the compressor types page.
The price keeps moving
The electricity price behind that running cost is not fixed. It changes with DESNZ's non-domestic rate each quarter, so a cost worked out a year ago can be well off today's figure.
Once you have a figure, sending it to a distributor is the next step
A distributor still needs your free air delivery, your receiver size and your duty before they can quote properly.