Generator Wattage Calculator

Adjust the calculator values below

Minimum generator apparent-power rating 6.95 kVA
Total running load 3,050 W
All-at-once starting load 3,890 W
Design load for selected startup 3,890 W
Apparent power at design load 4.8625 kVA
Generator real-power rating at target capacity 5.557143 kW
Largest single startup increase 800 W
Power factor 0.8
Target operating capacity 70%
Active appliance slots 6
6.95 kVA
Minimum generator apparent-power rating Reference household load; simultaneous startup; 0.8 power factor; 70% target capacity
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Generator Wattage Calculator

Use this generator wattage with appliance 1 running watts, appliance 1 starting watts, and appliance 2 running watts to get fast results, understand...

Separate running load from startup load

Running watts are the power an appliance uses after startup. Starting watts are its total brief startup demand, not an amount to add again. The calculator sums running values and either sums all starting values or adds the largest single startup increase to the total running load when starts are staggered.

Convert design watts into a generator kVA rating

Apparent power in kVA equals the selected design watts divided by power factor and 1,000. The minimum generator rating then divides that apparent power by the target operating-capacity fraction. At 0.8 power factor and 70% capacity, a 3,890 W design load requires about 6.95 kVA.

Verify the final selection against equipment data

Nameplate starting watts, voltage, phase, frequency, waveform quality, altitude, temperature, fuel type, derating, transfer equipment, duty cycle, and manufacturer surge-duration limits can change the suitable generator. Critical, medical, or code-regulated systems require review by the generator supplier or a qualified electrician.

Frequently asked questions

Common questions about running watts, starting watts, staggered startup, power factor, operating headroom, kVA sizing, unused appliance slots, and installation checks.

What is the difference between running and starting watts?

Running watts are the ongoing load after startup. Starting watts are the appliance's total brief startup demand. Do not enter only the extra startup watts.

How does staggered startup change generator size?

When only one appliance starts at a time, the design load is total running watts plus the largest single difference between an appliance's starting and running watts. Simultaneous startup instead uses the sum of all starting watts.

How is the minimum kVA rating calculated?

Divide the selected design watts by 1,000, the generator power factor, and the target operating-capacity fraction. This converts real load demand into the apparent-power nameplate rating with operating headroom.

Why is the suggested generator larger than the appliance watts?

Power factor and the target operating-capacity limit both increase the nameplate rating needed. The extra rating helps cover reactive load and avoids planning continuous operation at full capacity.

Can I leave an appliance slot unused?

Yes. Set both the running and starting values for that slot to 0. A partially completed pair is rejected so it cannot silently distort the total.

What else should I verify before buying a generator?

Confirm voltage, phase, frequency, waveform quality, surge duration, altitude and temperature derating, fuel, duty cycle, transfer equipment, and manufacturer data. Use a qualified electrician for critical or regulated installations.