Wondering what size air compressor do I need? This free air compressor cfm calculator matches compressor CFM to your air tools, sizes the tank, picks single vs two-stage, and checks the electrical circuit -- a complete air compressor buying guide for the best air compressor size for home garage and shop use, including an air compressor for painting cars.
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Enter how many of each tool run at the same time. The cfm requirements for air tools below are average consumption (SCFM at working PSI) from published air-tool charts, already weighted by typical duty cycle.
| Air tool | Avg. consumption | Typical duty | Qty in use |
|---|---|---|---|
| Brad Nailer (18 ga) | 0.5 SCFM @ 90 PSI | 15% | |
| Finish Nailer (16 ga) | 1.5 SCFM @ 90 PSI | 15% | |
| Framing Nailer | 2.5 SCFM @ 90 PSI | 15% | |
| Impact Wrench (1/2 in) | 4.5 SCFM @ 90 PSI | 25% | |
| Impact Wrench (3/4 in) | 8 SCFM @ 90 PSI | 25% | |
| Air Ratchet (3/8 in) | 4 SCFM @ 90 PSI | 25% | |
| Orbital Sander (6 in) | 7.5 SCFM @ 90 PSI | 50% | |
| Die Grinder (1/4 in) | 5 SCFM @ 90 PSI | 50% | |
| Angle Grinder (4-1/2 in) | 6.5 SCFM @ 90 PSI | 50% | |
| HVLP Spray Gun | 9.5 SCFM @ 50 PSI | 70% | |
| Conventional Spray Gun | 7 SCFM @ 50 PSI | 50% | |
| Blow Gun | 3 SCFM @ 90 PSI | 20% | |
| Tire Inflator | 1.5 SCFM @ 90 PSI | 30% | |
| Air Hammer / Chisel | 4 SCFM @ 90 PSI | 25% |
SCFM vs CFM: CFM is just a volume rate, but air expands and contracts with pressure and temperature, so raw CFM cannot be compared. SCFM pins the measurement to standard conditions -- 14.7 psia, 68°F, 36% relative humidity (the common US CAGI/ASME standard) -- so one compressor can be fairly compared with another. Always shop by the SCFM at 90 PSI rating.
Use this scfm to cfm conversion (ideal gas law) either way: measured ACFM at your pressure and temperature becomes SCFM, or run it backwards as a cfm to scfm calculator.
What size air tank do I need? The tank is a buffer, not extra power: use 4-6 gallons of tank per CFM of compressor output for intermittent shop use (6-10 for continuous duty). Bigger tanks cut motor starts; they do not raise CFM.
Air compressor duty cycle is the share of time the pump can run without overheating. Standard single-stage pumps are typically rated 50-75% duty; running one flat-out all day cooks it. Match the pump to your real duty, and see how long will an air compressor run air tools on one tank charge below.
A single-stage pump compresses air once (max ~125 PSI). A two-stage pump compresses it twice, reaching ~175 PSI, running cooler and more efficiently. Rule of thumb: when do I need a two stage air compressor? -- when any tool needs over 125 PSI, or for sustained high-CFM work.
| Single-stage | Two-stage | |
|---|---|---|
| Max pressure | ~125 PSI | ~175 PSI |
| Best for | Intermittent use under 125 PSI | Over 125 PSI or 60%+ duty |
| Efficiency | Lower at high pressure | Higher, runs cooler |
| Cost | $150-$700 typical | $600-$1,800+ typical |
| Power | 120 V up to ~2 HP | Usually 240 V |
Air compressor electrical requirements, from NEC Table 430.248 full-load amps: what size breaker for air compressor duty, how many amps does an air compressor draw, and the air compressor wire size (copper, 60°C column). Wire is sized at 125% of full-load amps.
| Motor | Amps @ 120 V | Amps @ 240 V | Circuit @ 120 V (breaker / wire) | Circuit @ 240 V (breaker / wire) |
|---|---|---|---|---|
| 0.5 HP | 9.8 A | 4.9 A | 15 A / 14 AWG | 15 A / 14 AWG |
| 0.75 HP | 13.8 A | 6.9 A | 20 A / 12 AWG | 15 A / 14 AWG |
| 1 HP | 16 A | 8 A | 20 A / 12 AWG | 15 A / 14 AWG |
| 1.5 HP | 20 A | 10 A | 25 A / 10 AWG | 15 A / 14 AWG |
| 2 HP | 24 A | 12 A | 30 A / 10 AWG | 15 A / 14 AWG |
| 3 HP | 34 A | 17 A | 45 A / 6 AWG | 25 A / 10 AWG |
| 5 HP | 56 A | 28 A | 70 A / 4 AWG | 35 A / 8 AWG |
| 7.5 HP | 80 A | 40 A | 100 A / 1 AWG | 50 A / 6 AWG |
Oil vs oil free air compressor: oil-lubricated pumps are quieter and longer-lived but need oil changes; oil-free pumps are cheap, light and maintenance-free but loud and shorter-lived. How loud is an air compressor? Check the air compressor noise level db rating before you buy -- anything above 85 dB needs hearing protection.
Noise context: normal conversation ~60 dB; 85 dB risks hearing damage over an 8-hour day; 90 dB needs protection even for short jobs. Price bands are typical US street prices (estimates) for the pump class, not quotes.
Add up your tools' average air use, then add 30% headroom. Example: one framing nailer (2.5 CFM), one 1/2-inch impact wrench (4.5 CFM) and one orbital sander (7.5 CFM) average 5.3 SCFM together; with 30% headroom you need about 6.8 SCFM at 90 PSI. Pair that with at least a 30-gallon tank (27.3 gal at 4 gal/CFM), ideally a 60-gallon tank (41.0 gal at 6 gal/CFM), a 2.0 HP pump, and since the highest tool pressure is 90 PSI a single-stage 125 PSI compressor is enough.
Multiply each tool's rated CFM by how often it actually blows air (its duty cycle), add the tools that run at the same time, then add 25-30% headroom. In the worked example above the three tools average 5.3 SCFM, so a compressor rated for about 6.8 SCFM at 90 PSI covers them. Always compare the SCFM rating at 90 PSI, not the inflated displacement CFM.
A 1/2-inch impact wrench averages about 4.5 CFM at 90 PSI (25% duty cycle), and a 3/4-inch drive averages about 8.0 CFM at 90 PSI. Because impacts hit in bursts, a compressor rated around 6 SCFM at 90 PSI with a 20-gallon or larger tank runs a 1/2-inch gun comfortably in a home garage.
HVLP spray guns are the thirstiest common shop tool: about 9.5 SCFM at roughly 50 PSI inlet (70% duty cycle). Conventional guns need about 7.0 SCFM. For painting cars, size the compressor for the gun alone with 30% headroom -- about 12.4 SCFM -- on a 60-gallon tank, otherwise the pressure sags mid-panel.
A 6-inch orbital sander averages about 7.5 CFM at 90 PSI and runs near-continuously (~50% duty cycle), which makes sanders one of the hardest tools on a small compressor. If sanding is your main job, treat it as continuous duty: pick a two-stage pump or add tank (6+ gallons per CFM).
Nailers sip air: a brad nailer uses about 0.5 CFM at 90 PSI and a framing nailer about 2.5 CFM at 90 PSI, both at roughly 15% duty cycle. Almost any pancake or hot-dog compressor (2+ SCFM at 90 PSI) keeps up with a single nailer; the tank matters more than pump CFM here.
CFM is just a volume rate; SCFM pins it to standard conditions so compressors can be compared honestly. The common US (CAGI/ASME) standard is 14.7 psia, 68°F and 36% relative humidity (air density 0.075 lb/ft³). Always compare the SCFM rating at 90 PSI when you shop -- that is the number that tells you what the pump really delivers.
Use the ideal gas law: SCFM = ACFM × ((PSI+14.7)/14.7) × (527.67/(Temp°F+459.67)). Example: 5.0 ACFM measured at 90 psig and 80°F equals 34.8 SCFM. The converter in the SCFM vs CFM section above runs this both ways, ACFM to SCFM and SCFM to ACFM.
Use 4-6 gallons of tank per CFM of compressor output for intermittent shop use (6-10 for continuous duty). For the 6.8 SCFM example that is 27.3 gallons minimum -- a standard 30-gallon tank -- and 41.0 gallons ideal, i.e. a standard 60-gallon tank. Bigger tanks mean fewer motor starts, not more CFM. How long will an air compressor run air tools on one charge? A 30-gallon tank cycling between 95 and 125 PSI holds about 1.2 minutes of tool air at 6.8 SCFM before the motor restarts.
You need a two-stage pump when any tool requires more than 125 PSI, or when the compressor's maximum pressure must exceed 125 PSI (typical two-stage cut-out is 175 PSI). A two-stage is also the smart pick for sustained use -- roughly 10+ SCFM or 60%+ duty cycle -- because it runs cooler and more efficiently. Below 125 PSI and intermittent duty, single-stage is cheaper and simpler.
Size wire at 125% of the motor's full-load amps (NEC 430.22) and confirm with a licensed electrician. A 2.0 HP motor draws 12.0 A at 240 V, so use a 15 A double-pole breaker with 14 AWG copper; at 120 V it draws 24.0 A, needing a 30 A breaker with 10 AWG copper on a dedicated circuit. The electrical section below tables every common HP at 120/240 V -- how many amps an air compressor draws, the breaker, and the wire size.
Oil-lubricated pumps run quieter (about 70-80 dB), last longer, and suit sustained shop use, but need oil changes and a filter for paint work. Oil-free pumps are cheaper, lighter and maintenance-free, but louder (85-90 dB -- wear hearing protection) and wear out faster. For a home garage running a few hours a week, oil-free is fine; for daily shop use, buy oil-lubricated.
Method notes: tool CFM values are average consumption (SCFM at working PSI) from published air-tool consumption charts at ~90 PSI; add 30% headroom; tank rule 4-6 gal/CFM intermittent; pump rule ~3.5 SCFM per HP at 90 PSI (approximate -- always trust the compressor's SCFM rating over HP); electrical per NEC Table 430.248. Verify your exact tool's nameplate before buying.