Base consumption = (5000/10000) × 0.75 = 0.375 gal/hr at full load. At 50% load: 0.375 × 0.50 = 0.1875, adjusted by gasoline BTU factor = 0.37 gal/hr. 8 hours × 0.37 = 3.0 gallons × $3.50 = $10.50.

27,500W Diesel Generator at 75% Load

Inputs

Generator7,500W

Load75%

FuelDiesel ($4.00/gal)

Run Time24 hours

Result

Fuel Rate0.37 gal/hr

Total Fuel8.8 gallons

Total Cost$35.16

Cost per Day$35.16

Base = (7500/10000) × 0.75 = 0.5625 gal/hr at full load. Diesel efficiency factor = 120000/138000 = 0.87. At 75% load: 0.5625 × 0.75 / 0.87 = 0.37 gal/hr. Over 24 hours: 8.8 gal × $4.00 = $35.16.

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Frequently Asked Questions

How much fuel does a generator use per hour?

Fuel consumption depends on generator size and load. A 5,000W gasoline generator at 50% load uses about 0.37 gallons per hour. At full load, that increases to about 0.75 gal/hr. Diesel generators are 15–20% more efficient, while propane uses about 15% more fuel by volume.

3,000W at 50% load: ~0.22 gal/hr gasoline ($0.77/hr at $3.50/gal)
5,000W at 50% load: ~0.37 gal/hr gasoline ($1.30/hr)
7,500W at 50% load: ~0.56 gal/hr gasoline ($1.96/hr)
10,000W at 50% load: ~0.75 gal/hr gasoline ($2.63/hr)
Diesel uses ~15% less fuel than gasoline for the same output

Generator Size	25% Load	50% Load	75% Load	Full Load
3,000W	0.11 gal/hr	0.22 gal/hr	0.34 gal/hr	0.45 gal/hr
5,000W	0.19 gal/hr	0.37 gal/hr	0.56 gal/hr	0.75 gal/hr
7,500W	0.28 gal/hr	0.56 gal/hr	0.84 gal/hr	1.13 gal/hr
10,000W	0.37 gal/hr	0.75 gal/hr	1.13 gal/hr	1.50 gal/hr

How long will a generator run on a tank of gas?

Runtime depends on tank size, generator wattage, and load. A 5,000W generator with a 5-gallon tank at 50% load runs about 13.5 hours. At full load, the same setup lasts about 6.7 hours. Inverter generators are more efficient at partial loads.

3-gallon tank at 50% load (5kW): ~8.1 hours
5-gallon tank at 50% load (5kW): ~13.5 hours
8-gallon tank at 50% load (5kW): ~21.6 hours
Inverter generators: 20–40% better fuel economy at light loads
Never run a generator completely dry — stop with 10–15% fuel remaining

Is it cheaper to run a generator on propane or gasoline?

Propane costs less per gallon ($2–3 vs $3–4 for gasoline) but has fewer BTUs per gallon. A propane generator uses about 15% more fuel by volume. At typical prices, propane costs about the same per hour as gasoline, but offers cleaner emissions and indefinite fuel storage life.

Gasoline: 120,000 BTU/gal, $3–4/gal, ~6-month shelf life
Propane: 91,500 BTU/gal, $2–3/gal, indefinite shelf life
Diesel: 138,000 BTU/gal, $3.50–4.50/gal, 12–18 month shelf life
Natural gas: cheapest per BTU but requires utility connection
Propane wins for emergency standby due to unlimited storage life

What size generator do I need for my house?

A typical home during an outage needs 5,000–7,500W for essentials (fridge, sump pump, lights, phone charging) or 10,000–20,000W for whole-house backup including HVAC. List your essential appliances and add their wattages, then add 25% safety margin.

Refrigerator: 100–400W running, 1,200W starting surge
Sump pump: 800W running, 2,000W surge
Central AC (3-ton): 3,500W running, 7,000W surge
Well pump: 700–1,500W running, 2,000–4,000W surge
Add 25% to total for safety margin and future needs

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Last Updated: Jun 11, 2026

This calculator is provided for informational and educational purposes only. Results are estimates and should not be considered professional financial, medical, legal, or other advice. Always consult a qualified professional before making important decisions. UseCalcPro is not responsible for any actions taken based on calculator results.