Get the Numbers Right — The System Will Forgive Almost Everything Else
Compressor too small, pipe too narrow, receiver too tiny. These are the mistakes you pay for forever. Sizing is the part of compressed air design where the math actually matters — and where most installations get it wrong.
Start here if you're sizing a system or inherited one
There are four sizing questions, and people mix them up: how much CFM / m³/hr does the compressor make? How big should the receiver be? How big is the pipe? How big should the dryer and filters be? Each one has its own rule of thumb. Get all four right and the system runs quiet.
1. Compressor Sizing — How Much Air Do You Actually Need?
The nameplate of the compressor is not the capacity you'll get in real life. And the amount of air your tools need is rarely what the salesperson estimated. Here's how to do it properly.
Free Air Delivery (FAD) Explained
FAD is the real capacity. The nameplate often lies. Here's how to read the spec sheet without being fooled.
Pressure, Volume, Capacity Units
psi, bar, kPa, CFM, m³/hr, l/s — don't mix them up. With a unit converter table.
Compression of Air — What's Actually Happening
The physics. Why compressing air makes heat. Why nameplate kW is mostly heat, not air.
Coming soon: Compressor sizing methodology · How to measure existing air demand · Sizing for variable load profiles.
Just trying to buy a compressor?
This is the engineering version of sizing — the math, the units, what FAD actually means, why the nameplate kW is mostly heat. Useful if you're designing a system from scratch, or trying to make sense of the spec sheet you're holding. If shopping is your actual goal though, head to the air compressor buying guide — same numbers, just as a few questions instead of a few formulas.
2. Receiver Sizing — Bigger Is Almost Always Better
Of all the cheap upgrades you can do on a compressed air system, increasing the receiver size is my favorite. It does three good things at once — slower cycling, more stable pressure, lower energy — and there's almost no downside besides taking up floor space. Trust me, get the bigger one :)
Why Have an Air Receiver Anyway?
The water-tower analogy. Why a bigger tank gives you a quieter, more stable system AND saves energy. (Cas-classic from 2019.)
Air Receiver Sizing
Rules of thumb + the actual math. How big is big enough for your demand profile.
Coming soon: How to upgrade an undersized receiver · Multiple receivers vs one big one · Wet vs dry receiver placement.
3. Pipe Sizing — The Cheap Mistake That Pays Back Forever
A pipe sized too small in year 1 will be costing you energy in year 25. Pipe is cheap, downtime is not, and pressure drop compounds across the whole system. If in doubt, go one size up.
Compressed Air Pipe Sizing — The Right Way
How to pick the right pipe size. Rule of thumb plus the calculation.
Pipe Sizing — Worked Example
A full calculation example with numbers in both psi/bar.
Compressed Air Piping — Materials & Layout
Steel, copper, stainless, plastic. What to use where, and where each fails.
Coming soon: Loop vs branch layout · Slope, drain points, and condensate · When to upgrade an existing pipe run.
4. Pressure Drop & Component Sizing
Every filter, dryer, fitting, and meter takes a little pressure with it. Add them up across a poorly-designed system and you'll lose 1.5 bar / 20 psi before the air gets to the tool. Then someone turns up the compressor pressure to compensate — which wastes another ~10% of the energy bill.
Pressure Drop Fundamentals
What pressure drop is, where it comes from, why it costs you money.
Pressure Drop — Basics
Shorter intro.
Compressed Air Filters
Types, sizing, when to change them. The 5–10 psi drop nobody measures.
Compressed Air Dryer Selection
Refrigerated vs desiccant vs membrane. Sizing for your dewpoint target.
Coming soon: Dryer sizing for your climate · Filter staging (pre-filter, coalescing, particulate) · Pressure drop budget for the whole system.
Why sizing is the cheapest part of the job and saves the most money
The decisions in this section are pure math. They cost you a few hours of thinking up front, and they save you energy for the next 20 years. There's no downside to spending time on this.
Pipe is cheap, energy is not
A bigger pipe costs maybe 30% more in materials. The energy savings pay it back in 1–3 years. After that it's pure profit, for decades.
Receiver size affects everything
Storage volume sets your pressure stability, your control band, your compressor cycle frequency, and your peak demand handling. One number, four benefits.
Every 2 psi / 0.14 bar = ~1% energy
That's the rule. If your system runs 0.7 bar / 10 psi higher than it needs to, you're paying 5% more on your energy bill, year after year.
Sizing has an order of operations
Demand first, then storage, then pipe, then components. Doing it in any other order means you'll resize things twice.
Model It in the Simulator Before You Build It
Sizing is what the compressed air simulator does best. Model your demand profile, try different compressor sizes, different receiver volumes, different control strategies — and see the energy use before you spend a dollar on equipment. Coming late 2026.
- Test compressor sizing decisions against real demand profiles
- Compare receiver sizes side-by-side
- Model pressure drop across the whole system
- Try multi-compressor configurations
- Get the running cost numbers before you sign a PO
Got pressure drop or low capacity right now?
If your existing system can't reach setpoint, has pressure drop across the plant, or tools aren't getting enough air — that's a troubleshooting problem first, a redesign problem second. Start with low pressure troubleshooting or pressure drop troubleshooting, then come back here once you know whether it's design or fault.
Stuck on a sizing decision?
Drop the demand numbers and your situation in the Q&A — I'll usually point you to the right size and the right rule of thumb to use.