What Size Generator Do You Need to Run an Air Compressor?
By the Generator Size Calculator Team · Updated · 6 min read
Quick answer: Honda lists an air compressor at 1,000 running and 2,000 starting watts for 1/2 HP, 1,500 and 4,500 for 1 HP, 2,200 and 6,000 for 1.5 HP and 2,800 and 7,700 for 2 HP. The surge is the problem, so size for the starting watts: about 2,500 watts for 1/2 HP, 4,000 for 1 HP, 5,000 for 1.5 HP and 6,500 for 2 HP.
Air compressor watts by horsepower
| Air compressor | Running watts | Starting watts |
|---|---|---|
| 1/2 HP | 1,000 | 2,000 |
| 1 HP | 1,500 | 4,500 |
| 1 1/2 HP | 2,200 | 6,000 |
| 2 HP | 2,800 | 7,700 |
The motor needs a short burst of power to start, up to about three times its running watts or more, especially if it starts against pressure in the tank. Honda's guide also notes that motors draw less once running. See starting vs running watts.
Which generator size to choose
| Compressor | Generator needed |
|---|---|
| 1/2 HP (1,000 / 2,000 W) | 2,500 W |
| 1 HP (1,500 / 4,500 W) | 4,000 W |
| 1 1/2 HP (2,200 / 6,000 W) | 5,000 W |
| 2 HP (2,800 / 7,700 W) | 6,500 W |
These sizes keep the running load under 80% of rating and assume a starting capacity about 25% above the running rating. Confirm your generator's own starting watts, and compare in what a 5000-watt generator can run.
How to reduce the surge
- Start the compressor first, with nothing else on the generator.
- Let the tank bleed down so the motor does not start against full pressure.
- Use a longer hose and a smaller, quieter pancake compressor if you only need a nail gun.
- Use a heavy, short cord. A thin cord adds voltage drop and strains the motor. See the extension cord calculator.
Combine the compressor with saws, lights and more.
Run the generator outdoors, at least 20 feet from doors, windows and vents. Never in a garage or shed, even with the door open. See how far a generator should be from your house.
Frequently asked questions
What size generator do I need for a 1 HP air compressor?
Honda lists a 1 HP compressor at 1,500 running and 4,500 starting watts, so a 4,000-watt generator with a good starting capacity is a sensible size.
Can a 3500-watt generator run an air compressor?
A 1/2 HP compressor, yes. A 1 HP unit starts at about 4,500 watts, which is above what a 3,500-watt generator typically delivers.
Why does an air compressor need so many starting watts?
The motor has to spin up quickly, and if it starts against a full tank it works even harder.
Does the tank size change the generator size?
Not directly. The motor sets the watts. A larger tank makes the motor run less often.
Can I run a compressor and a nail gun on a small generator?
A small pancake compressor can run on a 2,000-watt inverter if its label is within the generator's peak rating.
Related calculators
Sources: Running and starting watts from the Honda generator wattage guide (air compressors). Generator sizes apply the 80% running rule and an assumed starting capacity about 25% above the running rating, so confirm your own generator and compressor labels.