Generator Runtime Calculator
Appliance Load Calculator
Common Appliance Wattage Reference
Typical running wattage for household appliances. Starting wattage may be 2-3x higher.
| Appliance | Running Watts | Starting Watts | Priority |
|---|---|---|---|
| Refrigerator | 150-400 | 1,200 | Essential |
| Freezer | 100-300 | 800 | Essential |
| Sump Pump (1/2 HP) | 800 | 2,000 | Essential |
| Window AC (10,000 BTU) | 1,200 | 3,600 | High |
| Central AC (3 ton) | 3,500 | 7,000 | High |
| Space Heater | 1,500 | 1,500 | Seasonal |
| Microwave | 1,000 | 1,000 | Medium |
| LED Lights (10 bulbs) | 100 | 100 | Essential |
| Phone Charger | 25 | 25 | Essential |
| Laptop | 60 | 60 | Medium |
| TV | 100-200 | 200 | Low |
| Well Pump (1/2 HP) | 750 | 2,000 | Essential |
How We Calculate This
This generator runtime calculator uses established formulas and industry-standard data to provide accurate estimates.
- Enter your specific values into the calculator fields above
- Our algorithm applies the relevant formulas using your inputs
- Results are calculated instantly in your browser — nothing is sent to a server
- Review the detailed breakdown to understand how each factor affects your result
These calculations are estimates based on standard formulas. For critical decisions, always consult a qualified professional.
How to Convert Oven Recipes to Air Fryer
Generator runtime depends on fuel tank size, fuel type, generator capacity, and the electrical load being powered. This calculator estimates runtime and fuel costs based on these factors.
The basic rule:
- A typical gas generator consumes roughly 0.75 gal/hr at 50% load per 5,000 watts
- Fuel consumption scales with load — running at 25% load uses ~40% less fuel than 50% load
- Diesel generators are approximately 20% more fuel-efficient than gasoline
These are estimates based on typical generator efficiency curves. Actual consumption varies by brand, model, altitude, and condition. Always check your generator's manual for specific fuel consumption ratings.
When Would You Use This Calculator?
This generator runtime calculator is designed for anyone who needs quick, reliable estimates without complex spreadsheets or professional consultations.
- When you need a quick estimate before committing to a purchase or project
- When comparing different options or scenarios side by side
- When planning a budget and need to understand potential costs
- When you want to verify a quote or estimate you've received from a professional
- When teaching or learning about the concepts behind these calculations
Frequently Asked Questions
How many hours will a generator run on a tank of gas?
A typical 5,000-watt generator with a 5-gallon tank runs about 6-8 hours at 50% load. Runtime varies significantly by load, generator efficiency, and fuel type. Running at 25% load can nearly double runtime.
How much gas does a generator use per hour?
A 5,000-watt gas generator uses roughly 0.6-0.8 gallons per hour at 50% load. Larger generators use more, and the rate increases significantly at higher loads. At full load, the same generator might use 1.0-1.2 gallons per hour.
Is diesel or gas more efficient for generators?
Diesel generators are typically 20-30% more fuel-efficient than gasoline generators. Diesel fuel also has a longer shelf life (12+ months vs 3-6 months for gas). However, diesel generators cost more upfront and are louder.
What size generator do I need for my house?
Most homes need 5,000-7,500 watts to run essentials (refrigerator, lights, phone chargers, sump pump). To run central AC, you typically need 10,000+ watts. Add up the wattage of appliances you need to run simultaneously.
Should I run my generator at full load?
No. Running at full load continuously reduces efficiency, increases fuel consumption, and shortens generator life. Aim for 25-75% load for optimal fuel efficiency and longevity. The ideal range is 50-75% of rated capacity.
How much fuel should I store for a generator?
For a 3-day emergency running a generator 8-12 hours per day, store 15-25 gallons of fuel. For a week, store 40-60 gallons. Use fuel stabilizer (like Sta-Bil) for stored gasoline and rotate stock every 6-12 months.