Generator Sizing Calculator
Size a generator for backup power — total load plus the 25% safety margin every engineer uses.
Free · No signup · By the analysts at Blackridge Research · Updated 2026-07-18
Inputs
Results
What this means
Adjust the inputs to calculate.
About the Generator Sizing Calculator
Generator sizing ensures reliable backup power.
The standard safety margin is 25% above total load.
Formula
Generator Size = Total Load × 1.25
- GS
- — Generator Size
- TL
- — Total Load
- SM
- — Safety Margin
How to use this calculator
- 1
Enter total load
Total electrical load in kilowatts (kW).
Example calculations
Commercial building generator
A commercial building has a total load of 200 kW.
Generator Size = 200 × 1.25 = 250 kW.
- Recommended generator size:
- 250 kW
- Safety margin:
- 25%
A 250 kW generator provides a 25% safety margin for the 200 kW building load.
Interpreting your results
Generator sizing ensures reliable power during outages.
A 25% safety margin is standard for most applications.
Need the market data behind this calculator?
The Generator Sizing Calculator is only as good as its inputs. Blackridge Research publishes syndicated market reports with vetted market sizes, growth rates, and competitive landscapes across 40+ industries — and builds custom studies when the shelf report doesn't exist.
Industry applications
Business
- Backup power planning: size generator for critical loads.
- Construction planning: size temporary power generators.
- Disaster recovery: plan backup power capacity.
Construction
- Temporary power: size generators for construction sites.
- Permanent installations: size building backup generators.
Research
- Power analysis: determine backup power requirements.
- Feasibility studies: assess power needs.
Common mistakes to avoid
-
✗ Forgetting motor start-up surge
Motors draw 2-6× normal current on start-up.
-
✗ Ignoring future expansion
Size for planned future load increases.
Frequently asked questions
›What is the standard generator safety margin?
25% is the standard margin for most applications.
›What is a good generator size?
Size for total load plus 25% safety margin.
Glossary
- Generator:
- A device that converts mechanical energy to electrical energy.
- Load:
- The electrical power consumed by equipment.
- Start-up surge:
- The extra current drawn when a motor starts.
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