A refrigerator does not run at full power all the time. The compressor cycles on and off based on the internal temperature, so the actual average power draw is much lower than the rated wattage. This calculator uses the duty cycle to give you an honest runtime estimate — not the worst-case number from the rating plate alone.
Refrigerator Power Draw by Type
| Fridge Type | Compressor Watts | Avg Watts (40% duty) | Runtime on 100Ah 12V |
|---|---|---|---|
| 12V camping fridge (40L) | 35-45W | 14-18W | 38-49 hours |
| 12V camping fridge (60L) | 45-65W | 18-26W | 26-38 hours |
| Dometic/Engel (80L) | 55-80W | 22-32W | 21-31 hours |
| Mini fridge (residential) | 80-120W | 32-48W | 14-21 hours |
| Standard fridge (through inverter) | 120-200W | 48-80W | 8.5-14 hours |
| Full-size fridge/freezer (inverter) | 150-300W | 60-120W | 5.7-11 hours |
Runtimes assume 80% DoD and 90% efficiency. DC fridges connected directly to 12V skip the inverter loss, getting about 10% more runtime than AC fridges of the same wattage.
Example: Keeping a Fridge Running During a Power Outage
Your power goes out and you need to keep the kitchen fridge running. The fridge nameplate says 150W, but the compressor only runs about 35-40% of the time in normal conditions. Average draw: 150 x 0.38 = 57W.
You have a 200Ah 12V LiFePO4 battery and a 1,000W pure sine wave inverter (90% efficiency). Usable energy: 200 x 12 x 0.80 x 0.90 = 1,728Wh. Accounting for the inverter: 1,728 x 0.90 = 1,555Wh available at the AC outlet.
Runtime: 1,555 / 57 = 27.3 hours. That covers most outages with room to spare.
Tips to extend runtime: pre-cool the fridge to its coldest setting before the power goes out, avoid opening the door, and place frozen water bottles inside as thermal mass. Each of these can extend runtime by 10-20% by reducing the duty cycle.
Frequently Asked Questions
Adding solar to keep your fridge running indefinitely? The <a href="/solar/how-many-batteries-for-solar-system">solar battery count calculator</a> sizes a complete off-grid system.
The key to accurate fridge runtime calculations is the duty cycle — not the nameplate wattage alone. Measure your fridge's actual duty cycle with a kill-a-watt meter for the best estimate, or use 35-40% as a starting point for indoor use and 50-60% for warm environments.
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Written and maintained by Dan Dadovic, Developer & Off-Grid Energy Enthusiast. On the energy side, Dan has hands-on experience with residential solar panel installation, DIY battery bank construction, off-grid power systems, and wind power — all from building and maintaining his own systems..
Disclaimer: Calculator results are estimates based on theoretical formulas. Actual performance varies with temperature, battery age, load patterns, and equipment condition. For critical electrical work, consult a licensed electrician.