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Generator Calculator

Size your generator before you buy or rent. Undersized generators stall on motor start-up; oversized ones waste fuel. Use the calculators below to estimate your load, cross-check against our generator wattage chart, and you'll know the wattage you actually need.

These calculators are provided to help you determine the size of generator required for your specific needs. They are intended to assist in general estimates only. Please consult a sales rep for generator sizing.

Need help sizing a generator for your job? Call our sales team at 561-964-4949.

What Size Generator Do I Need?

Add up the running watts of everything that will run at the same time, then enter the largest additional starting (surge) watts of any single motor-driven tool — the extra it draws for a moment at startup. The generator needs to carry the running total continuously and the running total plus that surge at peak.

—Min. running watts
—Min. starting watts
—≈ kW at peak
—≈ kVA (PF 0.8)

Guidance only — starting loads, altitude, and duty cycle all matter. Our sales team will confirm the right unit for your job.

Required Power

To calculate the power you need, enter the voltage and amps required for your job, along with the power factor and phase.

—Power (kVA)
—Power (kW)
Show the math
  • Power (kVA) = (Voltage × Amps × Phase Factor) ÷ 1000
  • Power (kW) = Power (kVA) × Power Factor
  • Use a phase factor of 1 for single-phase and 1.732 for three-phase

Calculating Amps

To calculate how many amps you can get out of a generator, enter the generator size in kVA, the voltage required for your job, and the phase.

—Available amps (A)
Show the math
  • Amps (A) = (Generator kVA × 1000) ÷ (Phase Factor × Voltage)
  • Use a phase factor of 1 for single-phase and 1.732 for three-phase

From Wattage to the Right Machine

Once you know your load, remember the rule that catches most people out: electric motors draw two to three times their running watts at start-up, and the calculator has to cover the largest single starting load on top of everything already running. Our team sizes generators for contractors every day — call 561-964-4949 or send our parts team a request and we'll confirm the match. Already own one? We stock genuine generator parts and OEM service and repair kits to keep it running.