Last updated: 2026-11-08

Backup Generator Fuel Usage

Backup generator calculator: estimate diesel or biodiesel fuel use and cost for a standby generator over your outage runtime, by size, load, and conditions.

How much fuel will your backup generator burn during an outage? Enter the generator size, load, the runtime you need to cover, and the fuel type (diesel or biodiesel) to get hourly fuel use, the total fuel to have on hand, and running cost, with adjustments for temperature and altitude so you don't run dry mid-outage.

Key Features

Hourly and total fuel usage
Cost estimation at typical fuel prices
Environmental adjustments for altitude and temperature
Quick presets for home and business scenarios

Presets

Generator

Generator Size (kW)

Rated power output of your generator

Load Factor (%)

35% of rated capacity

25-35% typical for essential loads, 50-70% for comfort loads

Runtime

Runtime (hours)

Expected continuous runtime duration

Fuel Type

Biodiesel uses ~7% more fuel than diesel

Environment

Temperature (°C)

Ambient operating temperature affects efficiency

Altitude (meters)

Higher altitude reduces air density and engine efficiency

Guide

How much fuel will my backup generator burn, and how long will it run?

Why load factor — not tank size — decides runtime, with this calculator's own presets worked out: 4.8 gallons for an 8-hour standard home outage, 14.0 for a 12-hour winter storm.

Read the guide