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Runtime Calculator
Will a power station run your essentials through an outage? Check the boxes, adjust the watts and hours to match your own appliances, and the dashboard updates instantly.
1. Your outage loads
Wattages are typical estimates from Champion's generator wattage chart (checked 2026-10-07): running = middle of the published range, starting = top of the starting range. Your appliance's nameplate or a plug-in meter beats any estimate. "Duty %" is how much of the time it actually runs; defaults are our assumptions.
| Use | Appliance | Qty | Running W | Starting W | Hours/day | Duty % |
|---|---|---|---|---|---|---|
| Refrigerator (full size)Typical: 150-400 W running, 800-1,200 W startingCompressor cycles on and off. 33% duty is our assumption; your EnergyGuide label (kWh/yr ÷ 8.76 = average watts) is better. | ||||||
| Freezer (chest or upright)Typical: 100-500 W running, 500-1,000 W startingDuty cycle is our assumption. | ||||||
| Sump pump, 1/3 HPTypical: 500-800 W running, 1,000-1,600 W startingPump run time depends entirely on how much water comes in. 10% is a placeholder; raise it for heavy rain. | ||||||
| Sump pump, 1/2 HPTypical: 800-1,050 W running, 1,300-2,150 W startingSame caveat as above. Check the pump's nameplate. | ||||||
| Furnace blower fan, 1/2 HPTypical: 300-800 W running, 800-1,600 W startingGas furnaces still need power for the blower and controls. Hardwired furnaces need a transfer switch or inlet installed by an electrician. | ||||||
| Well pump, 1/2 HPTypical: 750-1,000 W running, 1,500-2,000 W startingMany well pumps are 240V and hardwired; check yours. Duty is our assumption. | ||||||
| CPAP (no heated humidifier)Typical: 30-60 WCheck your machine's power supply rating. Not medical advice; ask your provider about an outage plan. | ||||||
| CPAP with heated humidifierTypical: 60-120 WTurning off the humidifier and heated tube cuts power use a lot. | ||||||
| Internet router / modemTypical: 10-20 W | ||||||
| LED light bulb (each)Typical: 8-15 W | ||||||
| Phone / laptop chargerTypical: 20-100 W | ||||||
| TV (32-55 inch)Typical: 80-400 WNewer LED TVs are usually near the low end; check the label. | ||||||
| Ceiling fanTypical: 15-75 W | ||||||
| Home security systemTypical: 15-40 W | ||||||
| MicrowaveTypical: 600-1,200 WUses lots of power briefly. The label's input watts are higher than its cooking watts. | ||||||
| Window AC (5,000 BTU)Typical: 450-600 W running, 900-1,200 W startingDuty is our assumption. Central AC (2,000 W+ running) is beyond most portable stations. | ||||||
| Space heaterTypical: 750-1,500 WResistive heat drains a battery fast. Treat as a short-term option only. |
2. Power dashboard
Appliances use 0 Wh per day. After 85% inverter efficiency, the battery must supply 0 Wh per day.
Capacity tiers
- ~1 kWh class-
- ~2 kWh class-
- ~3.6-4 kWh class-
- ~8 kWh (expanded)-
- ~12 kWh (expanded)-
Models in our dataset that fit
Capacity covers your outage and rated output covers your running watts and surge, using manufacturers' published specs (checked 2026-10-07). Doesn't account for 240V needs or hardwired loads.
How the math works
The calculator follows the same approach generator makers publish for sizing: add up running watts, then add the single largest extra starting surge, because motors (fridge compressors, pumps, blowers) briefly draw several times their running power when they start (Champion, Honda). Honda's guide notes you can avoid stacking surges by starting big motors one at a time.
- Running watts = sum of (running W × quantity) for every checked load, as if everything were on at once. That's a conservative worst case.
- Peak (surge) watts = running watts + the largest single (starting W − running W) among checked loads.
- Daily energy (Wh) = sum of (running W × quantity × hours/day × duty %).
- Battery Wh needed = daily energy × days ÷ 0.85. The 85% figure is our stated assumption for AC inverter losses. Real efficiency varies by model and load, and is usually worse at very light loads.
- Tier fit: green means the tier covers your outage with at least 10% to spare; amber means it's within 10%; red means it falls short. "Lasts" estimates how many days of your daily load that capacity covers.
- Model fit requires capacity ≥ battery Wh needed, rated AC output ≥ running watts, and published surge ≥ peak watts. If a manufacturer doesn't publish surge, we compare peak watts against rated output.
Safety first. A power station can run plug-in appliances from its own outlets. Powering hardwired loads (a furnace, well pump, or home circuits) needs a transfer switch or power inlet installed by a licensed electrician. Never plug a power source into a wall outlet to backfeed your house. For medical devices, talk with your provider about an outage plan, as Ready.gov recommends.
Sources
- Champion Power Equipment, Generator Wattage Chart: running and starting watt ranges for every preset (checked 2026-10-07).
- Honda Power Equipment, What Size Generator Do I Need?: running vs starting watts method (checked 2026-10-07).
- ENERGY STAR, Refrigerators: refrigerator efficiency and sizing background (checked 2026-10-07).
- Power station capacities, outputs, and surge ratings: each model's official page, listed in our cost per kWh comparison (checked 2026-10-07).
Related: How big a power station do you need for a refrigerator? · Power station sizing guide