Generator Run Time Calculator - Fuel Consumption Estimator
How long will your generator run during a power outage? Calculate precise fuel consumption and runtime for Propane, Diesel, and Gasoline generators based on load and tank size.
Generator System
System Specifications
Different fuels have different efficiency rates
Nameplate rating on your unit
Propane tanks only filled to 80% capacity for safety
Typical home: 50% during outage
Fuel Efficiency
Diesel is most efficient, gasoline least efficient
Smart Tank Monitor
Track fuel levels from your phone. Never run out unexpectedly.
Maintenance Kit
Keep your generator running during extended outages.
Complete Generator Runtime & Fuel Guide
Understanding Generator Fuel Consumption
Generator fuel consumption rate varies significantly based on the type of fuel, generator size, and electrical load. Understanding these factors helps you plan for extended power outages and budget for fuel costs accurately.
Fuel Consumption Rates (per kW per Hour):
Diesel (Most Efficient)
0.07 gal/kW/hr
A 22kW diesel generator at 50% load uses ~0.77 gallons per hour
Propane (Popular)
0.11 gal/kW/hr
A 22kW propane generator at 50% load uses ~1.21 gallons per hour
Gasoline (Least Efficient)
0.14 gal/kW/hr
A 22kW gas generator at 50% load uses ~1.54 gallons per hour
Note: These are approximate rates. Actual consumption varies by manufacturer, engine efficiency, and environmental conditions.
Fuel Type Comparison
Each fuel type has unique advantages and disadvantages for standby power generation:
| Factor | Propane | Diesel | Gasoline |
|---|---|---|---|
| Fuel Efficiency | Moderate | Excellent | Poor |
| Shelf Life | Indefinite | 1-2 years | 6-12 months |
| Cold Weather Start | Good | Requires glow plugs | Excellent |
| Maintenance | Low | Moderate | Moderate |
| Fuel Storage | Requires tank | Tank or cans | Easy (gas cans) |
| Availability in Crisis | Good (tanks pre-filled) | May be limited | Often scarce |
| Price (per gallon) | $3.00-4.00 | $3.50-4.50 | $3.00-4.00 |
Calculating Your Fuel Needs
Accurate fuel planning prevents running out of power during extended outages. Follow this step-by-step process:
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1
Determine Your Generator Size
Check the nameplate on your generator unit for the kilowatt (kW) rating. Common residential sizes: 7kW, 10kW, 14kW, 20kW, 22kW. Whole-house systems typically range from 15-25kW.
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2
Estimate Your Load Percentage
Most homes run at 40-60% of generator capacity during outages. Running only essentials (refrigerator, lights, furnace): 25-40%. Running most appliances including AC: 60-80%. Maximum load (all circuits): 100%.
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3
Calculate Hourly Consumption
Formula: (Generator kW × Load% × Fuel Rate) = Gallons Per Hour
Example: 22kW at 50% load with propane: 22 × 0.50 × 0.11 = 1.21 gal/hr
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4
Account for Tank Capacity Limits
Propane tanks are filled to 80% for safety (thermal expansion). A 500-gallon propane tank holds 400 usable gallons. Diesel and gas tanks can use 95% capacity.
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5
Calculate Total Runtime
Formula: Usable Gallons ÷ Gallons Per Hour = Total Hours
Example: 400 gallons ÷ 1.21 gal/hr = 331 hours (13.8 days)
Fuel Storage Best Practices
Propane Storage
- Indefinite shelf life - won't degrade
- Store tanks outdoors in well-ventilated area
- Check for leaks annually with soapy water
- Tanks only filled to 80% capacity
- Level ground, away from building (10+ feet)
Diesel Storage
- 12-18 month shelf life untreated
- Add fuel stabilizer for longer storage
- Store in approved fuel tank or cans
- Keep cool, away from direct sunlight
- Prevent algae growth with biocide additive
Gasoline Storage
- 3-6 month shelf life (very short)
- Mandatory stabilizer for storage >30 days
- Use only approved red gas cans
- Store away from living spaces
- Rotate stock every 6 months
Frequently Asked Questions
Q: How long will a 500-gallon propane tank power my home?
A: A 500-gallon propane tank holds 400 usable gallons (80% fill). With a 22kW generator at 50% load (typical), you'll use about 1.21 gallons per hour. This provides approximately 331 hours (13-14 days) of continuous runtime. Reducing load to 25% can extend this to 25+ days.
Q: Is diesel or propane better for generators?
A: Diesel is 30-40% more fuel-efficient, making it cheaper to operate long-term. However, propane has indefinite storage life versus diesel's 12-18 months, making propane better for emergency preparedness. Diesel engines also require more maintenance (oil changes, filters) but are more durable for commercial applications.
Q: How much does it cost to run a generator per day?
A: At 2025 fuel prices ($3.50/gallon average), a 22kW generator at 50% load costs: Propane: $102/day (29 gal × $3.50) | Diesel: $65/day (18.5 gal × $3.50) | Gasoline: $129/day (37 gal × $3.50). Costs vary significantly with local fuel prices and actual load.
Q: Can I run my generator 24/7 during an outage?
A: Yes, modern standby generators are designed for continuous operation. However, perform these maintenance tasks: Check oil level every 24 hours (add if low), change oil every 100-200 hours of runtime, inspect air filter every 2-3 days, ensure adequate cooling airflow, and give the generator a break if possible (a few hours off every few days).
Q: How do I reduce my generator fuel consumption?
A: (1) Reduce electrical load - turn off non-essential appliances and lights, (2) Use programmable thermostat to moderate HVAC usage, (3) Avoid running high-wattage appliances simultaneously, (4) Keep generator well-maintained (clean air filter, fresh oil), (5) Consider load-shedding - rotate which circuits are powered, (6) Insulate home to reduce heating/cooling needs.
Pro Tips for Extended Outages
- Stock extra oil and filters: Change oil every 100 hours (every 4 days of 24/7 operation). Keep 3-4 oil changes worth on hand.
- Install a fuel gauge: Smart tank monitors connect to your phone, alerting you before running empty.
- Plan fuel delivery early: During major outages, propane and diesel delivery can be delayed 1-2 weeks. Arrange delivery when tank hits 30%.
- Consider dual-fuel generators: Units that run on propane OR gasoline provide flexibility if one fuel source becomes unavailable.