Portable Air Compressors: How to Size a Towable for the Tools You Actually Run
Sizing a portable air compressor really comes down to one question: what tools are you running, and at what pressure? Get that right, and the machine practically picks itself. Get it wrong, and you either end up with more compressor than the job needs, or a unit that leaves your tools starved for air on site. The number in the model name is a starting point, not an answer, and this guide walks through why.
Start With Your Tools, Not the Compressor
Most contractors who call us already have a model number in mind, and that's usually backwards. The right order is tools first, pressure second, and the machine last.
Here's how we build that number:
- List every tool that runs at the same time. Not every tool you own, just the ones that will be open together during the worst part of the job.
- Get each tool's air consumption at your working pressure. Check the data plate or the manufacturer's sheet. A 90 lb pavement breaker and a 60 lb breaker are nowhere near the same draw, and two brands of the same size tool can differ too.
- Add them up, then add headroom. We generally add roughly 25 percent to the calculated draw, the same buffer we use when sizing a shop system, because it keeps the machine off its limit all day and absorbs the hose length and fitting restrictions that eat into what actually reaches the tool.
- Confirm the pressure you actually need. This is the step people skip most often, and it changes everything about which machine is right for you. More on that below.
If you want to work through the underlying math on CFM, PSI, and horsepower, our guide on how to size an air compressor covers it in detail. The same logic applies to portables, with one important wrinkle.
The CFM in the Model Name Is Not the CFM You Get
Here's what catches a lot of buyers off guard. On a rotary screw portable, flow and pressure trade against each other, so raising the pressure setting drops the delivered CFM. Same machine, same day, a completely different number.
Two examples from Atlas Copco's own published data:
- The XATS 250 KD8 delivers 250 CFM at 100 psi, but turn it up to 150 psi and that drops to 189 CFM. Both figures are honest: the "250" in the name is just the low pressure figure.
- The E-Air H185 VSD delivers 191.5 CFM at 87 psi, 172.5 CFM at 100 psi, 160.4 CFM at 125 psi, 143.4 CFM at 150 psi, and 130.3 CFM at 174 psi, which works out to a 32 percent swing across the machine's own pressure range.
So when someone tells you they need "a 250," the first question is at what pressure. If the answer is 150 psi, a 250-class machine may leave them short of what they actually need.
This is also why Atlas Copco's PACE system matters. PACE stands for Pressure Adjusted through Cognitive Electronics, and it lets you dial in the working pressure from the controller in small increments instead of being locked into one fixed setting. The XATS 250 adjusts in 1 psi steps across 100 to 150 psi, and the E-Air units adjust in 2 psi steps, so one machine ends up covering a range of jobs instead of just one.
Diesel or Electric?
Every portable in our lineup is a rotary screw, so the real decision is what drives it.
Diesel goes anywhere, because it doesn't need power on site. That covers most jobsites, which is why the XAS and X-Air units are the default choice for general construction. The tradeoff for that freedom is fuel, engine maintenance, and emissions hardware.
Electric makes sense when you have power available on site and noise or fumes are a problem. The E-Air VSD range runs on 380V to 460V with no diesel engine at all, which brings three real advantages:
- No engine PM. No fuel filters, no engine oil changes, no DEF, no emissions aftertreatment to service.
- Quieter. The E-Air units are rated at 61 to 65 dB(A) sound pressure at 23 feet, versus roughly 71 to 76 dB(A) for diesel towables in the same flow class measured the same way, and that gap matters on noise restricted sites and indoor work.
- Lighter. The H185 VSD weighs 1,648 lb. Diesel machines in a comparable flow class run heavier because of the engine, cooling package, and fuel.
One caution on comparing noise ratings across brands: some spec sheets publish sound pressure at a stated distance, while others publish sound power, which is a different measurement and produces a bigger number. Make sure you're comparing like with like before deciding one machine is louder than another.
Towable or Truck Mounted?
Most portables ride on a trailer with a tow bar, and if you're pulling the machine from job to job behind a truck, that's exactly what you want.
Skid and utility mount units solve a different problem. The U110 Utility Mount takes the XAS 110 class and packages it on a support frame that bolts to a service truck deck instead of towing behind one. It delivers 110 CFM from a 25 HP Kubota D902 and weighs 1,103 lb crated, and tire service rigs, utility line crews, and oilfield service trucks tend to pick it over a trailer because it frees up the hitch and keeps the machine with the truck at all times.
If your crew is towing a trailer anyway, take the towable. If the truck is the job, look at the utility mount.
The Atlas Copco Portable Lineup at A1
Here's the full range we stock, sorted by flow. Every CFM figure below is listed with the pressure it applies at, because as covered above, that's the only way the number actually means anything.
| Model | Drive | Free Air Delivery | Pressure Range | Power | Best For |
|---|---|---|---|---|---|
| XAS 110 KD8 | Diesel, towable | 95 CFM at 100 psi | 100 to 125 psi | Kubota, 24.8 HP | One or two air tools, small crews |
| U110 Utility Mount | Diesel, skid | 110 CFM | 29 to 128 psi | Kubota D902, 25 HP | Service truck on board air |
| E-Air H185 VSD | Electric, towable | 191.5 CFM at 87 psi down to 130.3 CFM at 174 psi | 72.5 to 174 psi | 35 HP motor | Noise restricted and indoor work |
| X-Air 185-100 | Diesel, towable | 189 CFM at 100 psi | 58 to 125 psi | Kubota D1803-T, 49.6 HP | Breakers and general construction, cold weather package |
| E-Air H250 VSD | Electric, towable | 233 CFM at low pressure down to 177 CFM at high pressure | Up to 190 psi | 50 HP motor | High pressure work with power on site |
| XATS 250 KD8 | Diesel, towable | 250 CFM at 100 psi, 189 CFM at 150 psi | 100 to 150 psi, PACE | Kubota, 65 HP | Jobs that need pressure above 125 psi |
| X-Air 375-150 | Diesel, towable | 375 CFM | 72 to 150 psi | Caterpillar C4.4, 88 HP | Multi tool crews, rental ready |
| XAS 400-150 PACE JD | Diesel, towable | Up to 410 CFM | 100 to 150 psi, PACE | John Deere T4F, 134 HP | Large crews and sustained high demand |
A few details worth knowing about the larger diesels: the XAS 400-150 PACE carries a low fuel shutdown, so the operator doesn't have to re-prime the fuel system after running dry, and it ships with a 5 year extended factory warranty on the John Deere engine. The X-Air 185-100 burns 2.37 gallons per hour at full load from a 27 gallon tank, which gets you through most of a shift before refueling.
Browse the full range on our portable air compressors and diesel air compressors pages.
What About Freight?
Towable compressors ship by freight, and the cost varies by destination. We quote freight per shipment right alongside the machine, so you see the full delivered number before you commit, with no surprise charges after the fact.
If you would rather arrange your own carrier or pick the unit up, that works too. Just tell us when you request the quote and we'll price it that way.
Should You Rent or Buy?
Our honest answer: buy if your utilization is steady, rent for one-off jobs.
If the machine sits on your yard between jobs and goes out a few times a year, renting is usually the cheaper path, and you skip the maintenance entirely. If it's out most weeks, though, rental invoices add up fast, and you end up paying someone else's depreciation on a machine you'll never own. Contractors who run air daily almost always come out ahead buying instead.
The middle case is worth thinking through carefully. If you're renting the same class of machine six or more times a year, it's worth running the numbers on a purchase. We're happy to help you work through that math with no sales push either way.
Frequently Asked Questions
How many CFM do I need to run a jackhammer?
It depends on the size of the breaker, so check the tool's data plate rather than relying on a rule of thumb. A single large pavement breaker is generally comfortable on a 185 CFM-class machine, and running two together pushes you toward the 375 CFM class. Tell us the specific tools and we'll size it for you.
Does a portable compressor lose CFM at higher pressure?
Yes, and significantly. The E-Air H185 drops from 191.5 CFM at 87 psi to 130.3 CFM at 174 psi. Always check the flow at the pressure you'll actually run, not the headline number.
What does PACE mean on an Atlas Copco compressor?
PACE stands for Pressure Adjusted through Cognitive Electronics. It lets you set the working pressure from the controller in small increments, so one machine covers a pressure range instead of being fixed at a single setting. The XATS 250 adjusts in 1 psi steps, the E-Air units in 2 psi steps.
Is an electric portable compressor worth it over diesel?
It is if you have power available at the job. You give up the go-anywhere freedom of diesel and gain lower noise, no engine maintenance, no fuel, and less weight, which makes it often the only workable option on noise-restricted or indoor sites.
Can I mount a portable compressor on my service truck?
Yes. The U110 Utility Mount is built for exactly that, using a support frame that bolts to a truck deck rather than a trailer. It delivers 110 CFM and weighs 1,103 lb crated.
Get Sized Correctly the First Time
The difference between the right portable and the wrong one usually comes down to one conversation about which tools are running together and at what pressure. That conversation is free, and it takes about five minutes.
Talk to a real compressor expert. Free consultations on sizing, installation, and replacement parts. Same-day response, no chatbots, no runaround.