Fuel Consumption Calculator
Estimate fuel usage and operational costs for your diesel generator. Our technical tool uses specific fuel consumption (SFC) metrics to provide accurate budgeting data.
Operational Parameters
Calculated Power Output
At 75% load, your generator is producing approximately 0 kW of real power.
Consumption Summary
Book a generator fuel & health audit
If your generator burns noticeably more than this estimate, worn injectors, clogged filters or poor loading are usually costing you money every month. Our engineers will measure actual consumption on site and show you where it is going.
Technical Guide to Diesel Generator Fuel Consumption
Fuel is the single largest operating expense for any diesel generator system. Understanding exactly how much diesel your engine consumes is vital for budgeting and operational planning.
The Science of SFC
Engineers measure fuel efficiency using a metric called Specific Fuel Consumption (SFC). This is the mass of fuel consumed per unit of power produced. A modern diesel engine typically consumes between 0.24 and 0.28 liters of diesel for every kilowatt-hour (kWh) generated, though that figure worsens noticeably below 50% load, which is why the calculator above uses a sliding SFC scale rather than a single fixed number.
Worked Example: 150kVA Generator, 8-Hour Outage
Take a 150kVA generator running at 80% load with a 0.8 power factor. Actual electrical output is generator size × power factor × load percentage: 150 × 0.8 × 0.8 = 96kW. At 80% load the engine sits in its efficient operating band, so SFC stays at the base rate of roughly 0.27 litres per kWh, giving fuel burn of 96 × 0.27 ≈ 25.9 litres per hour.
Over an 8-hour outage, that's approximately 207 litres of diesel consumed. At a typical pump price of KES 165 per litre, the fuel cost for that single outage comes to roughly KES 34,000. Running the same generator at just 30% load instead — a common mistake when a unit is oversized for the connected equipment — pushes SFC up to around 0.30 L/kWh even though the kW output is lower, which is the efficiency penalty behind "wet stacking" and why correct generator sizing affects fuel budgets directly, not just equipment longevity.
Factors Affecting Consumption
1. Load Profile
Running a generator at its peak efficiency point (70-80% load) provides the best "liters per kilowatt" ratio. Low load operation increases SFC significantly.
2. Maintenance Condition
Dirty air filters and worn fuel injectors can cause poor atomization and restricted airflow, directly increasing fuel consumption by up to 15%.
Frequently Asked Questions
How much fuel does a 100kVA generator use?
At 75% load, a 100kVA generator typically consumes about 16-18 liters of diesel per hour.
Does low power factor increase fuel usage?
Yes. A low power factor increases the current the alternator must produce, creating more heat and resistance, requiring more fuel.
Why does running a generator at low load waste fuel?
Diesel engines are most fuel-efficient in their 70-80% load band. Below roughly 50% load, incomplete combustion raises SFC, so the same kW of useful output costs noticeably more diesel — on top of causing wet-stacking if sustained for long periods.
Professional Audit
Calculators provide estimates. For mission-critical facilities, a physical load audit is mandatory to ensure 100% capacity accuracy.
Quick answer
This calculator estimates how many litres per hour your diesel generator burns and what that costs in Kenyan shillings, using a sliding specific fuel consumption (SFC) scale tied to your load percentage. Enter your generator rating in kVA, your load percentage, runtime and current diesel pump price to get an instant fuel cost figure. For a 100 kVA generator running at 75% load with diesel at KES
Converting diesel litres to kWh — and why it matters for budgeting
The relationship between diesel consumed and kilowatt-hours generated is what engineers call the specific fuel consumption (SFC) rate. A well-maintained diesel engine in its efficient load band converts roughly one litre of diesel into approximately 3.5–4.2 kWh of electrical output. Put another way, divide your total litres burned by your kWh generated to get your actual SFC; anything above 0.30 L/kWh is a warning sign worth investigating.
This conversion is useful when comparing diesel generator cost against grid tariffs from Kenya Power. If your KPLC rate is, say, KES 20 per kWh and your generator is producing power at KES 35–45 per kWh in fuel alone (before oil, filters and wear), the cost gap makes a strong case for keeping generator runtime as short and efficient as possible — which means correct load management and a well-maintained engine.
- Litre to kWh conversion: divide kWh output by litres consumed to get efficiency in kWh/L
- A healthy modern engine: 3.5–4.2 kWh per litre at 70–80% load
- Below 50% load: efficiency drops to 3.0 kWh per litre or less, raising cost per kWh significantly
- Above 90% load for sustained periods: thermal stress shortens engine life even if fuel efficiency looks acceptable
Why your actual fuel consumption may be higher than this calculator shows
The figures this tool produces are based on manufacturer SFC data for a generator in good condition at the stated load. In practice, several common faults push real-world consumption 10–25% above that baseline without triggering an obvious alarm.
Dirty or clogged air filters starve the engine of combustion air, forcing more fuel through injectors to achieve the same power output. Worn or partially blocked fuel injectors produce poor atomisation — fuel droplets that are too large to combust completely — resulting in both higher consumption and black exhaust smoke. A faulty cooling system that allows the engine to run hotter than its design temperature also increases fuel burn. Finally, a generator that is significantly oversized for its connected load will spend most of its runtime in the low-efficiency zone described above, paying a fuel penalty every hour it runs.
- Black or grey exhaust smoke: usually incomplete combustion from injector or air filter problems
- Fuel consumption creeping up month on month: often the first measurable sign of injector wear
- Generator running cool or hunting at idle: possible thermostat or governor fault affecting efficiency
- Oversized unit at low load: consider a load audit to confirm whether a correctly sized unit would reduce running costs
An on-site fuel and health audit measures actual consumption under real load conditions, compares it
kVA to kW — understanding the calculator's power output figure
Several search terms landing on this page relate to the kVA-to-kW relationship, so it is worth explaining clearly. kVA is the apparent power rating stamped on the generator nameplate. kW is the real (useful) power actually delivered to your load. The difference between them is the power factor — a number between 0 and 1 that reflects how efficiently your connected equipment uses electrical current.
Real power (kW) = kVA × power factor. Most commercial and industrial loads in Kenya operate at a power factor of 0.8, which is why a 100 kVA generator is often described as an 80 kW machine. The calculator uses 0.8 as its default assumption. If your site has a high proportion of motors, air conditioning or UPS systems, the actual power factor may differ — and a lower power factor means the alternator works harder for the same kW output, which affects both fuel consumption and alternator temperature.
- 100 kVA at 0.8 PF = 80 kW real power output
- 200 kVA at 0.8 PF = 160 kW real power output
- If your power factor is below 0.8, fuel consumption per usable kWh rises further
- Power factor correction capacitors can improve this on sites with heavy motor loads
Frequently asked questions
How do I calculate diesel generator fuel consumption per hour manually?
Multiply your generator's kW output (kVA × power factor × load fraction) by the SFC rate for your load level, typically 0.27–0.30 L/kWh. For example, a 200 kVA generator at 75% load and 0.8 power factor produces 120 kW; at 0.27 L/kWh that is roughly 32 litres per hour.
What is a normal litres-per-hour figure for a 100 kVA generator?
At 75% load with a 0.8 power factor, a 100 kVA generator typically burns 16–18 litres of diesel per hour in good condition. Consumption above 20 litres per hour at the same load usually indicates a maintenance issue worth investigating.
Why does my generator use more fuel than the calculator estimates?
The most common causes are clogged air filters, worn fuel injectors, a faulty thermostat causing the engine to run outside its design temperature, or the generator being significantly underloaded. A site fuel audit with flow measurement will pinpoint which factor is responsible.
Can I use this calculator for a petrol or gas generator?
No — this tool is calibrated for diesel engines using diesel-specific SFC data. Petrol and gas engines have different heat values and combustion characteristics, so the figures would not be accurate for those fuel types.
How often should fuel consumption be checked on a standby generator?
Consumption should be recorded at every service visit and compared against previous readings. PowerProKe's maintenance programme services generators every 250 running hours or every three months, whichever comes first, and fuel consumption data is included in the written service report produced after each visit.