generator tool
Generator Wattage Calculator
Compare running watts with starting watts for a generator load.
Starting watts represent the additional surge above running watts. Use equipment label values when available; generator running and peak ratings are separate.
Generator wattage estimate
1800 W running
Starting surge requirement: 1500 W. Estimated peak requirement: 3000 W. These are planning estimates, not an installation guarantee.
Generator wattage guide
Compare running and starting watts
This page documents the current calculator exactly. It does not calculate watts from volts, amps, phase, or power factor; its inputs are running watts, starting watts, and safety headroom.
Formula
starting surge = max(0, starting watts − running watts)
running capacity = running watts × (1 + headroom ÷ 100)
estimated peak = running watts + starting surge
Worked examples
Resistive-style load: 1,500 running watts and 1,500 starting watts produce 0 W starting surge. With 20% headroom, the running capacity estimate is 1,800 W and estimated peak is 1,500 W.
Motor-style load: 800 running watts and 2,000 starting watts produce a 1,200 W starting surge. With 20% headroom, the running capacity estimate is 960 W and estimated peak is 2,000 W.
Practical considerations
Calculated watts are only one part of generator loading. Startup timing, motor characteristics, voltage requirements, load balance, and the generator's nameplate ratings also matter. Use equipment labels when available and keep continuous and peak ratings separate.
Frequently asked questions
What does this Generator Wattage Calculator calculate?
It accepts running watts, starting watts, and safety headroom. It reports running watts with headroom, the starting surge requirement, and estimated peak watts.
Does this calculator use volts, amps, phase, or power factor?
No. Those are not inputs in the current Generator Wattage Calculator. Enter running and starting watt values from the equipment or load information.
How is the starting surge calculated?
The calculator uses max(0, starting watts − running watts). It does not add all starting watt values together.
Does the result replace generator nameplate information?
No. Compare the estimate with the generator's rated running and peak outputs and confirm the load requirements with equipment documentation.
Important assumptions
This is a planning estimate, not a guarantee of performance. Real equipment varies with temperature, age, power quality, duty cycle, wiring, and manufacturer specifications.