Rotary Screw Air Compressor Sizing and Sales
Industrial Rotary Screw Air Compressors, Sized Right the First Time
Sized to your real demand, not the nameplate so your plant air runs efficiently from 5 to 350 HP, fixed speed or VSD.
What size rotary screw compressor does my plant actually need?
A rotary screw air compressor is the workhorse for plants that run continuous or near-continuous production air, and sizing it starts with demand: total the cfm of the tools and processes that run at the same time, add roughly 30 percent headroom for leaks and future growth, then match that number to your required pressure. A plant drawing 80 cfm simultaneous should shop around 105 cfm, which lands in the 25 HP class at 125 psi. Use the estimator below for a starting range, then have an engineer verify it against your actual demand profile before you buy.
CFM and HP estimator
Enter what you know. The estimate uses 12 cfm per general station, applies your duty cycle, and adds 30 percent headroom. It is a starting range, not a substitute for a demand study. For a fuller walkthrough, use the CFM calculator or read our guide on how much CFM you need.
Sizing reference: demand to HP class
| Demand after headroom | HP class | Typical Sullair line |
|---|---|---|
| Up to 40 cfm | 5 to 10 HP | ES-6 S-energy or ShopTek |
| 40 to 110 cfm | 15 to 25 HP | S-energy 15-25 |
| 110 to 270 cfm | 30 to 60 HP | S-energy 3000PB-4500VB |
| 270 to 470 cfm | 75 to 100 HP | SN Series |
| 470 to 1,000 cfm | 125 to 200 HP | LS Series |
| 1,000 cfm and up | 250 to 350 HP | TS Series |
Sullair rotary screw lines we stock and service
-
Sullair ShopTek
- Power
- 5 to 100 HP
- Flow
- 16 to 434 cfm
- Type
- Lubricated rotary screw
- Best for
- Shops and light industrial duty
-
Sullair ES-6 S-energy
- Power
- 5 to 10 HP
- Flow
- 18 to 40 cfm
- Type
- Lubricated rotary screw
- Best for
- Small shops moving up from piston
-
Sullair S-energy 15-25
- Power
- 15 to 25 HP
- Flow
- 60 to 110 cfm
- Type
- Lubricated rotary screw
- Best for
- Multi-bay shops and small plants
-
Sullair S-energy 3000PB-4500VB
- Power
- 40 to 60 HP
- Flow
- 175 to 270 cfm
- Type
- Lubricated rotary screw
- Best for
- Mid-size manufacturing plants
-
Sullair SN Series
- Power
- 75 to 100 HP
- Flow
- 330 to 470 cfm
- Type
- Lubricated rotary screw
- Best for
- Continuous production air
-
Sullair LS Series
- Power
- 125 to 200 HP
- Flow
- 540 to 1,000 cfm
- Type
- Lubricated rotary screw
- Best for
- Large plants and base load
-
Sullair TS Series
- Power
- 250 to 350 HP
- Flow
- 1,150 to 1,600 cfm
- Type
- Two-stage lubricated rotary screw
- Best for
- High-volume 24/7 operations
How to choose: VSD vs fixed speed, duty cycle, and stages
- Variable speed (VSD) vs fixed speed. Pick fixed speed if your demand is steady and high, and variable speed if demand swings between shifts or across the day. A VSD unit ramps motor speed to match demand, which typically saves 20 to 35 percent in energy for plants with variable load, while a fixed-speed machine is cheaper upfront and most efficient when it runs fully loaded. Many plants pair a fixed-speed base machine with a VSD trim unit.
- Duty cycle. A rotary screw wants to run loaded. If your compressor loads and unloads many times an hour it wastes energy and wears controls, so size for the load it will actually carry, not the nameplate maximum.
- Single stage vs two stage. Larger horsepower and higher pressure often favor a two-stage airend for efficiency. Compare the tradeoffs in our single stage vs two stage air compressor guide before you spec.
- Pressure. Every 2 psi of extra pressure costs about 1 percent more energy, so spec the lowest pressure your most demanding process actually needs. Confirm your numbers with the CFM calculator.
Beyond the machine
- Air that touches product or people belongs on the oil free compressor page instead.
- See how plants like yours run air in manufacturing applications, food and beverage, and automotive.
- Installation, compressor service and repair, and compressed air audits keep the system efficient after startup.
- Bridge a shutdown or a peak with air compressor rentals.
- Every machine is backed by 14 service locations across WI, IL, MN, and MO, including Milwaukee, Chicago, and Minneapolis.
- Confirm your numbers with the CFM calculator or read single stage vs two stage air compressors.
- 24/7 emergency response, under 2 hour average
- Factory-trained technicians
- 14 Midwest locations across WI, IL, MN, and MO
- Family owned since 1978, Sullair dealer since 1984
Rotary screw sizing questions, answered first
How many CFM do I need per air tool or station?
Plan on 10 to 15 cfm for a general production station, then use the manufacturer ratings printed on each tool where you have them: typical published ratings run about 5 cfm for a half-inch impact wrench at normal duty, 20 to 25 cfm continuous for a die grinder, and 35 cfm or more for a blast cabinet. Total the tools that run at the same time, not everything you own, and multiply each by its duty cycle before adding headroom.
Why add 30 percent headroom instead of buying exactly what I use?
Because leaks, growth, and control response eat the margin fast. A typical plant loses 20 to 30 percent of its air to leaks, and a compressor sized to 100 percent of demand short-cycles and dies young. Sizing to roughly 130 percent of measured demand lets the machine load and unload properly and leaves room to add a station without buying again.
Should I pick a fixed speed or variable speed (VSD) rotary screw?
Pick fixed speed if your demand is steady and high, and variable speed if demand swings between shifts or across the day; that is the whole decision. Many plants do best with a fixed-speed base machine plus a VSD trim unit. A no-cost demand review of a week of your plant data answers this definitively.
How much pressure should I spec, 125 psi or higher?
Spec the lowest pressure your most demanding process actually needs, because every 2 psi of extra pressure costs about 1 percent more energy. Most plants run fine at 100 to 125 psi. If one process needs more, it is usually cheaper to give it a dedicated booster than to raise the whole plant header.
Free calculators from our engineers. Every formula is shown, nothing is gated, and the defaults are realistic so you see an answer immediately.
- VSD Savings Calculator Estimate what a variable speed drive saves at your load profile before you commit. Open the calculator
- Pressure Reduction Savings Every 2 PSI of discharge pressure is about 1 percent of compressor energy. See your number. Open the calculator
- SCFM to ACFM Converter Convert between standard and actual CFM for your altitude and inlet conditions. Open the calculator
Get a sizing recommendation from an engineer
Send your estimator result and we will verify it against your real demand profile before you buy, then quote the right Sullair line. Compressor down right now? We answer 24/7.
Request a quote or book an air audit
Send your estimator result for an engineer's sizing review and we will verify it against your real demand profile before you buy. Urgent? Call 800.825.3222, answered 24/7.
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