🔋 Generator Fuel Calculator
Enter your generator's kVA rating, tank size, load percentage, and fuel price to instantly see runtime from a full tank, litres consumed per hour, daily running cost, and the fuel stockpile needed for planned outages. Supports petrol, diesel, and LPG - includes an appliance load calculator to size your generator correctly.
🔋 Generator Fuel Calculator
Fuel Type
🔌 Load Planner
Add appliances to calculate total load and required generator size.
📦 Fuel Stockpile Planner
Calculate how much fuel to store for emergencies and planned outages.
📐 Generator Fuel Calculations
Fuel Consumption Formula
Load Factor Impact on Fuel Use
Generator Sizing Rules
❓ Frequently Asked Questions
Generator Fuel Calculator - Runtime, Consumption Rates & Fuel Storage Guide
Power outages are unpredictable, but your fuel planning doesn't have to be. Whether you're sizing a generator for a home, calculating running costs for a business, or planning a fuel stockpile ahead of a monsoon season, knowing your generator's exact consumption rate and runtime is essential. This calculator handles all three scenarios - from a single outage estimate to a multi-day stockpile plan.
Fuel Consumption Formula - How Generator Burn Rate Is Calculated
Generator fuel consumption is measured in litres per hour (L/hr) and depends on three factors: the rated capacity (kVA), the actual load applied as a percentage of capacity, and the fuel type. The standard formula:
Fuel consumption (L/hr) = Generator kVA × Load% × Consumption factor
Typical consumption factors: Petrol = 0.33–0.38 L/kVA/hr. Diesel = 0.25–0.30 L/kVA/hr. LPG ≈ similar to petrol by volume.
At 75% load, a 5 kVA petrol generator: 5 × 0.75 × 0.35 = 1.31 L/hr. The same 5 kVA diesel generator: 5 × 0.75 × 0.27 ≈ 1.01 L/hr - roughly 23% more efficient than petrol.
Diesel vs Petrol vs LPG - Which Generator Fuel Type Is Right for You?
Diesel Generator
- 20–30% more fuel-efficient than petrol
- Diesel engines last longer - typically 20,000–30,000 hours
- Better for heavy loads and continuous operation
- Quieter at higher kVA ratings
- More expensive to buy upfront (₹30,000–1 lakh premium)
- Best for: daily use during long outages (4+ hours), commercial use, high-load applications
Petrol Generator
- Lower upfront cost - same kVA costs 30–50% less than diesel
- Quieter at lower kVA ratings (1–3 kVA)
- Easier to start in cold conditions
- Better for light/occasional use
- Petrol shelf life shorter (3–6 months)
- Best for: infrequent use, 1–4 hour outages, small homes without AC
Sizing Your Generator - What Load Do You Actually Need?
The most common generator sizing mistake is accounting only for running wattage without factoring in startup surge wattage. Motors (in ACs, refrigerators, water pumps) require 2–3× their running wattage to start. A generator that's adequately sized for running loads can trip or stall when starting a compressor motor.
Typical appliance wattage (running / startup) for an Indian home:
- 1.5-ton inverter AC: 1,200W running / 1,500W startup (inverter ACs have low startup surge)
- 1.5-ton non-inverter AC: 1,500W running / 4,000–5,000W startup
- Refrigerator (double door): 200W running / 500–800W startup
- Ceiling fan: 70W running / 70W startup (no surge)
- LED bulbs (4×10W): 40W running / 40W startup
- LED TV (43 inch): 90W running / 90W startup
- Water pump (0.5 HP): 375W running / 750–1,000W startup
Recommended sizing: add up all running watts, add the single largest startup surge (not all at once), multiply total by 1.25 for a safety buffer, then choose the nearest standard generator size above that figure.
The Optimal Load Percentage - Why 75% Is the Sweet Spot
Running a generator at the right load percentage significantly affects fuel efficiency, engine wear, and lifespan:
- Below 30% load: "Light loading" causes inefficient combustion, oil fouling, and in diesel engines, wet stacking - unburnt fuel accumulates in the exhaust system. Avoid prolonged light loading, especially in diesel generators.
- 50–80% load: The optimal operating range. Good fuel efficiency, proper combustion temperature, manageable heat output, and adequate headroom for startup surges.
- Above 90–100% load: Significantly increases heat, accelerates engine wear, and leaves no headroom for surge loads. Short-term spikes are fine; sustained 100% load shortens engine life.
The 75% load point is where most generator manufacturers rate their performance specs - it's also where fuel consumption per kWh output is lowest for most engine types.
Fuel Storage - How Long Petrol and Diesel Stay Usable
Stored fuel degrades over time, particularly petrol which oxidises faster than diesel. Planning a stockpile requires knowing your storage limits:
- Petrol: 3–6 months without additives. Up to 12 months with a fuel stabiliser (available at auto parts shops). Store in approved metal jerry cans or HDPE containers. Keep cool, dark, and away from heat sources.
- Diesel: 6–12 months without treatment. Up to 24 months with a biocide (prevents microbial growth in the tank) and stabiliser. Diesel degrades by oxidation and microbial contamination - particularly in humid climates like India.
- Always rotate your fuel stockpile - use stored fuel and replace it regularly rather than letting it sit for 1–2 years. Label containers with the fill date.
- Never store fuel inside a home, near electrical panels, or in direct sunlight. Fuel storage at home is regulated - check local rules for maximum permitted quantities.