Event Power Calculator

Generator sizing applies a second multiplier on top of the 20% safety margin: it adds a further 25% to the margin-adjusted total to cover surge and inrush current when motors and other equipment start up. So Generator Size (kW) is roughly your raw wattage times 1.2 times 1.25, then divided by 1,000 — not just the margin-adjusted total on its own.

Generator kW is the real power figure after the surge margin is applied. Generator kVA divides that kW figure by an assumed 0.8 power factor, since generators are rated in apparent power (kVA) to account for the phase difference between voltage and current that mixed AC, lighting, and motor loads introduce. Use kVA when comparing against a generator's nameplate rating, since that's how most rental generators are labeled.

Circuit count isn't just total amps divided by 20 — it assumes each circuit is only loaded to 80% of its rated capacity for continuous use (1,920 usable watts on a 20A/120V circuit), matching OSHA's own Table S-4 (29 CFR 1910.304(b)(4)(ii)(B)), which caps a 20A circuit's connected load at 16A. That 80% limit comes from the National Electrical Code's continuous-load rule (NFPA 70 §§210.19(A)/210.20(A)) and is not an extra safety buffer you can ignore. That's why Circuits Needed can look higher than a naive amp-to-circuit conversion would suggest.

It's a rough diesel-generator rule of thumb — about 7 gallons per hour for every 100 kW of generator size — useful for a ballpark tank-size and refueling-interval estimate. Actual burn rate depends heavily on your generator's specific model, how much of its rated capacity you're actually loading, and ambient conditions, so confirm real fuel consumption numbers with your generator rental vendor before finalizing logistics for a multi-day event.