The Three Questions You Need to Answer
Buying the wrong air compressor is expensive. Too small and it can’t keep up with demand. Too large and you’ve wasted money on power and space. Get these three things right and you’ll have a compressor that works hard for decades.
1. What’s Your Maximum Air Demand? (CFM)
CFM stands for cubic feet per minute—the volume of air delivered at a given pressure. This is the most important spec.
How to calculate it:
Add up the CFM requirements of all the tools you’ll run at the same time. You won’t run everything simultaneously in real life, but you want enough headroom that the motor doesn’t struggle.
Common tool demands:
– Air drill: 5-8 CFM
– Impact wrench: 7-10 CFM
– Angle grinder: 8-12 CFM
– Spray gun: 10-15 CFM
– Nail gun: 2-3 CFM
– Orbital sander: 6-8 CFM
Example: If you typically run a spray gun (12 CFM) and an impact wrench (8 CFM) at the same time, you need at least 20 CFM. Add 20% for safety headroom, and you’re looking for a 24+ CFM compressor.
Pro tip: If you plan to add tools later, buy bigger now. A compressor that’s slightly oversized is better than one that’s constantly maxed out.
2. What Pressure Do You Need? (PSI)
Most pneumatic tools run at 90-120 PSI (pounds per square inch). Check your tool manuals.
– Nail guns: 80-100 PSI
– Impact wrenches: 90-120 PSI
– Spray guns: 40-60 PSI
– Angle grinders: 90 PSI
– Chisels: 90 PSI
Most workshop compressors deliver 125-175 PSI, which is fine. You regulate down to what your tools need using a regulator. Look for a compressor rated for at least 125 PSI—anything less and you won’t have enough pressure reserve.
3. What Size Tank Do You Need?
The tank stores air and helps the motor cycle less frequently. Bigger tanks mean the motor runs less, which saves energy and extends the motor’s life.
Tank sizing rule of thumb:
– Small workshop, light use (nails, small drills): 20-30 litres
– Medium workshop, regular use (spray guns, impact wrenches): 50-100 litres
– Heavy workshop, continuous use (multiple tools, all day): 150+ litres
Bigger tanks also smooth out pressure dips when multiple tools run simultaneously. If your tank is too small, you’ll hear the motor cycle frantically as it tries to keep up.
Example: If you calculated you need 24 CFM, a 50-litre tank gives you about 2 minutes of tool runtime before the motor kicks back in. That’s usually comfortable.
Oil vs Oil-Free: Which Should You Choose?
Oil-lubricated compressors:
– ✓ Longer lifespan (5,000+ hours typical)
– ✓ Quieter operation
– ✓ Better power efficiency
– ✗ Require maintenance (oil changes, filter cleaning)
– ✗ Can contaminate air for sensitive applications
Oil-free compressors:
– ✓ No maintenance
– ✓ Clean air (safe for paint, food, electronics)
– ✓ Portable (no oil to spill)
– ✗ Shorter lifespan (2,000-3,000 hours)
– ✗ Louder, hotter operation
For most workshops: Oil-lubricated is the better investment. The cost of occasional maintenance is less than replacing an oil-free unit every few years.
Single-Stage vs Two-Stage
– Single-stage: Simpler, less expensive, typical max 125 PSI, good for general workshop use
– Two-stage: More complex, higher efficiency, typical max 175+ PSI, better for heavy continuous use
Unless you need over 125 PSI or run tools all day, single-stage is fine.
Brand and Build Quality
You get what you pay for. Budget brands fail sooner and cost more to run. Established brands like SIP, Festo, and Parker (for components) have proven reliability.
Signs of quality:
– Cast iron cylinder and head (not aluminium)
– Ball-bearing motor
– Heavy-duty pump
– Solid tank construction (not thin sheet metal)
– Good warranty (2+ years)
Popular Options for Different Uses
Light workshop, occasional use:
– 20-30 litre, 100-115 CFM, oil-free
– Budget: £300-500
Regular workshop use:
– 50-100 litre, 150-200 CFM, oil-lubricated, single-stage
– Budget: £600-1,200
Heavy workshop, all-day use:
– 150+ litre, 250+ CFM, oil-lubricated, two-stage
– Budget: £1,500+
Don’t Forget the Extras
Once you have your compressor, you’ll need:
– Regulators to adjust pressure for different tools
– Moisture traps to remove condensation
– Quality hoses rated for your pressure (look for brands like Parker and PCL)
– Fittings that won’t leak (we stock ASCO, Festo, and Crouzet options)
A poorly maintained system with cheap fittings will underperform and waste energy, even if your compressor is top-notch.
Still Not Sure?
Every workshop is different. If you’d like to talk through your specific needs—what tools you use, how often, and what space you have—we’re happy to help. We stock compressors and all the hoses, fittings, and regulators you’ll need to build a reliable system.
Call us on 01474 334537 or visit our workshop supplies section to see our full range.
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