Generator sizing calculator

Calculate emergency power capacity requirements

Try it now

Live calculator

Live preview

Loading calculator...

The Generator Sizing Calculator helps electrical engineers and facility managers determine appropriate generator sizes for emergency and standby power systems. Calculate required generator capacity based on connected loads and safety factors.

Proper generator sizing ensures adequate power supply during utility outages while avoiding unnecessary oversizing that increases cost and reduces efficiency. Generators must handle starting loads, motor inrush currents, and provide capacity margin.

Enter connected load in kW and safety factor percentage to calculate required generator capacity. The calculator estimates kVA requirements assuming typical power factor and recommends standard generator sizes for emergency power applications.

Features

Everything you need

Generator capacity calculations
kW and kVA determination
Safety factor adjustments
Standard size recommendations
Power factor considerations
Emergency power sizing
Load factor support

How it works

Simple workflow

1
Enter total connected load in kW
2
Specify safety factor percentage
3
Review calculated required capacity
4
See estimated kVA requirement
5
Select standard generator size

Use cases

Built for real-world scenarios

Emergency power design

Size generators for emergency and standby power systems in commercial buildings.

Load planning

Determine generator capacity requirements for new facilities and equipment additions.

Code compliance

Verify generator sizing meets code requirements for emergency power systems.

Cost estimation

Estimate generator costs based on required capacity for project budgeting.

FAQ

Frequently asked questions

Required Capacity = Connected Load × (1 + Safety Factor). Typical safety factors: 20-30% for general loads, 50-100% for motor loads. Add 25% for motor starting inrush.

Safety factors: 20-25% for general loads, 30-50% for mixed loads with motors, 50-100% for heavy motor loads. Higher factors provide more margin but increase generator size and cost.

kW is real power, kVA is apparent power. kVA = kW ÷ Power Factor. Generators are rated in kVA. Typical PF: 0.8-0.9. For 100 kW at 0.8 PF: kVA = 100 ÷ 0.8 = 125 kVA.

Motors have high starting currents (3-7× running current). Generator must handle starting loads. Consider motor starting method (across-the-line vs. soft-start) and sequence motor starts.

Have a suggestion?

We're always looking to improve our calculators. If you have ideas for new features, improvements, or found something that could work better, we'd love to hear from you.

Related tools