Generator fuel consumption calculator (diesel)
An estimate of how much diesel a generator burns per hour at your load, what it costs per day, and how long it runs on a tank.
Your numbers
The generatorHow you run it See your resultResult
Fuel per hour 4.14 galat 50% load, estimated from 100 kW Fuel per day 41.4 gal Fuel cost per day $165.60 Run time on a full tank 48.3 h Stop working this out by handFleetZap PM schedules open generator services on engine hours, and fuel logs record gallons and cost for each unit.
See FleetZap Maintenance · Try the demoThe formula
Fuel per hour ≈ Full-load fuel × (0.15 + 0.85 × Load) · Full-load fuel ≈ 0.072 gal per kW when unknown
A diesel generator still burns fuel with no load, so consumption doesn’t fall in a straight line to zero. This is a rough estimate: with no spec sheet, a 100 kW set at 50% load comes to about 4.1 gallons an hour. The maker’s fuel table for your model is always better; put its full-load figure in. The generator maintenance page covers the service intervals.
Using the numberWhat to do with it
- Running a diesel generator at very light load for long periods can cause wet stacking. Size the set to the job, or add load banks.
- Plan refueling from run time on a tank, with a margin, so a site never goes dark overnight.
- Log fuel per unit: a set that suddenly burns more at the same load needs a look at injectors, filters or the load itself.
Guides behind this calculator
Generator maintenance Generator maintenance cost and checklist Generator maintenance scheduleMore free calculators
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The heart of FleetZap, and everything a maintenance team needs in one place: work orders and preventive maintenance, inspections and the field app, plus a parts store with purchasing, compliance and certificate tracking, multi-location assets with a full lifecycle, and the KPIs that prove it’s working.
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Good to know
How much fuel does a 100 kW generator use?Roughly 7 gallons of diesel an hour at full load and about 4 at half load. Your model's spec sheet gives the exact figures.
Does a generator use less fuel at lower load?Yes, but not in proportion: it still burns fuel with no load. Half load usually takes a little over half the full-load fuel.
How long will a generator run on a tank?Divide the tank size by the fuel burn per hour at your load. A 200 gallon tank at about 4.1 gallons an hour lasts close to 49 hours.
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