Diesel Generator Sizing Calculator
Accurately size diesel generators for industrial, commercial, and backup power. Includes motor starting surge analysis and fuel consumption estimates.
Load Requirements
Environmental Factors
Power loss above 500ft
Power loss above 85°F
Required Diesel Generator
(-- kVA @ 0.8 PF)
Full Load Amps
-- A
Starting Surge
-- kVA
Estimated Fuel & Runtime
Based on approx 0.075 gal/kW/hr efficiency.
Standard Diesel Sizes
Diesel Generator Warning: Wet Stacking
Avoid oversizing excessively. Diesel generators perform best when loaded to at least 30-40% of their capacity. Running a diesel engine under light loads for extended periods can cause "wet stacking" — unburned fuel accumulating in the exhaust system. This leads to carbon buildup, reduced performance, and potential engine damage.
Recommended Diesel Equipment
Professional gear for your diesel power setup.
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How to Use the Diesel Generator Calculator
- Determine Base Load: Enter the total kilowatts (kW) of all non-motor loads (lights, heaters, computers). If you only know Amps, use our Amps to kW calculator first.
- Account for Motors: Enter the Horsepower (HP) of the largest motor that will start while the generator is running. Select the starting method (e.g., Direct On Line has a high surge, VFD has a low surge). This ensures the generator can handle the inrush current.
- Environmental Adjustment: Diesel engines need oxygen. High altitude (thin air) and high temperatures reduce power output. Enter your site conditions to apply the correct derating factor automatically.
- Check Phase & Fuel: Select whether you need Single-Phase (standard commercial/residential) or Three-Phase (industrial). Enter your fuel tank size to estimate runtime based on load.
- Analyze Results: The calculator provides a recommended generator size in kW and kVA. It includes a safety margin (default 20%) and accounts for the efficiency loss from environmental factors.