How the Generator Size Calculator Works
The calculator totals the running watts of equipment expected to operate at the same time. It adds a user-selected capacity margin and converts the resulting kW requirement to kVA using the entered generator power factor. Startup demand is screened separately so that a motor or compressor starting event is not hidden inside the normal running-load calculation.
How to Use the Calculator
Add each appliance, machine or equipment group, enter the quantity, running watts and starting watts per unit, then select the power factor and capacity margin you want to use for planning. The default startup scenario assumes the largest individual startup increment occurs while the other loads are already running. Use the alternative scenario only when simultaneous starting is a realistic operating condition.
Understanding kW and kVA
kW represents real power delivered to loads, while kVA represents apparent power. They are related by power factor. A generator labelled in kVA therefore cannot be treated as providing the same numerical value in kW unless the relevant power factor is 1.0. Always verify the manufacturer's actual rated kW and kVA.
Why Starting Loads Matter
Some electrical loads draw substantially more power while starting than after they reach normal operation. Pumps, refrigeration compressors, workshop machinery and some air-conditioning equipment are common examples. A generator that appears adequate from running watts alone may still perform poorly during startup.
Generator Sizing in Nigeria
Homes, offices, shops, factories and other businesses in Nigeria can use this tool to organize a generator requirement before comparing equipment. Actual selection should use the equipment nameplate data and generator manufacturer's specifications. Current generator and fuel prices should remain separate from the engineering calculation and can be handled through Finelib Prices and Finelib Match.
Related Energy & Power Calculators
Frequently Asked Questions
How do I calculate what size generator I need?
Add the running power of loads that may operate simultaneously, include a reasonable design margin, and separately check the generator's ability to handle the highest realistic startup or step-load demand.
What is the difference between generator kW and kVA?
kW is real power and kVA is apparent power. The relationship depends on power factor: kW = kVA × power factor.
Why do motors need extra generator capacity when starting?
Many motors and compressors draw higher current and power during startup. The generator and alternator must tolerate that temporary demand without unacceptable voltage or frequency drop.
Should I add the starting watts of every appliance together?
Not necessarily. It depends on whether those loads can realistically start at the same time. This calculator provides both a largest-starting-load scenario and an all-starting-together screening scenario.
Is a 10 kVA generator always equal to 10 kW?
No. At a power factor of 0.8, 10 kVA corresponds to 8 kW of real power. Always check the manufacturer's rated kW and kVA.
Should a generator normally run at 100% of its rating?
Generator loading should follow the manufacturer's operating and rating guidance. This calculator lets you add a planning margin rather than automatically assuming continuous operation at the calculated running load.
Does this calculator tell me which generator brand to buy?
No. It estimates a capacity requirement. Brand, model, prime or standby duty, fuel type, service support, installation and actual performance should be evaluated separately.