- Size is measured in watt-hours (Wh) - a 1,000Wh station runs a 100W device for about 8.5 hours
- Always add 25% to your calculation to account for inverter losses
- A full refrigerator uses roughly 1,200 Wh per day - this single item drives most home backup sizing
- Medical devices and sump pumps have special requirements beyond simple watt-hour math
- The free calculator below handles all of this automatically
Add up watt-hours for everything you need to run: a refrigerator uses 1,200Wh per day, lights 320Wh, router 120Wh, phone charging 50Wh. Multiply your total by 1.25 for efficiency losses. That number is your minimum capacity. A 2,000Wh station covers most household essentials for 24 hours.
The Watt-Hour Formula
Portable power stations are rated in watt-hours (Wh). A watt-hour is the amount of energy used by a 1-watt device running for one hour. A 100-watt device running for 10 hours uses 1,000 Wh.
The formula for sizing your system:
(Device Watts × Hours of Use) summed for all devices, × 1.25 for losses = minimum Wh capacity
The 1.25 multiplier accounts for inverter efficiency losses (typically 85-92%), battery discharge curves, and the fact that rated capacity decreases as batteries age. Always size up, not down.
Size Categories by Use Case
| Category | Capacity | Best For | Example Units |
|---|---|---|---|
| Power Bank | Under 150 Wh | Phone, GPS, headlamp charging for day trips | Anker Prime, Nitecore NB20000 |
| Compact | 150–500 Wh | Camping, light travel, CPAP without humidifier, brief home backup | EcoFlow River 2, Jackery Explorer 300 Plus |
| Mid-Size | 500–1,500 Wh | Home backup for 12-24 hours, RV, extended camping, medical devices | EcoFlow Delta 2, Jackery Explorer 1000 Plus, Bluetti AC180 |
| Large | 1,500–3,000 Wh | Home backup for 24-48 hours, full refrigerator plus devices | EcoFlow Delta 2 Max, Jackery Explorer 2000 Plus |
| Whole-Home | 3,000+ Wh | Extended outages, off-grid, multiple appliances for days | EcoFlow Delta Pro Ultra, Bluetti AC300 + B300 |
Common Appliance Watt-Hour Consumption
| Appliance | Wattage | Wh Per Day | Notes |
|---|---|---|---|
| Full-size Refrigerator | 100–400W cycling | ~1,200 Wh | Biggest single load for home backup |
| LED Lights (4 rooms) | 40–60W | ~320 Wh | Per 8 hours of use |
| Phone + Laptop | 30–65W | ~300 Wh | Laptop draw varies by use |
| Router + Modem | 15–25W | ~120 Wh | Keep internet alive priority |
| CPAP (no humidifier) | 30–60W | ~240 Wh/night | Pure sine wave required |
| CPAP + Humidifier | 60–120W | ~560 Wh/night | Size up significantly |
| TV (50 inch) | 80–150W | ~400 Wh | Per 4-5 hours of use |
| Window AC (5,000 BTU) | 500–700W | ~3,000 Wh | Requires large system |
| Sump Pump | 800–1,050W running | ~200 Wh | Surge 2,000–4,500W - unit selection critical |
Three Situations That Break Simple Math
Sump pumps have a startup surge that's 3-5x their running wattage. The watt-hour math may say 200 Wh per day, but if your power station can't handle the 3,000W+ surge at startup it won't run the pump at all. See our sump pump guide for unit selection.
Medical devices require a pure sine wave inverter specifically. Some medical equipment controllers will shut down or behave erratically on modified sine wave power even if the wattage is adequate. Every reputable portable power station uses pure sine wave, but verify before buying.
Well pumps can require 2,000-7,500W surge depending on HP rating. Most portable power stations cannot handle this - a generator or a specialized high-surge unit is typically required. See our well pump guide.
Use the Free Calculator
Rather than doing this math manually, the free calculator on our homepage handles all of it automatically. Select your appliances, choose your duration, and it calculates your minimum watt-hour requirement with the loss buffer applied - and flags any special surge or equipment requirements.
PoweredThrough earns commissions on qualifying purchases. We hold relationships with multiple competing brands simultaneously.
Frequently Asked Questions
How do I calculate what size power station I need?
Multiply each appliance's wattage by the hours you need to run it. Sum all devices. Multiply by 1.25 for inverter losses. That is your minimum watt-hour (Wh) capacity. Example: refrigerator at 1,200Wh + lights at 320Wh + router at 120Wh = 1,640Wh x 1.25 = 2,050Wh minimum.
What is a watt-hour?
A watt-hour (Wh) is the amount of energy used by a 1-watt device running for one hour. A 100W device running for 10 hours uses 1,000Wh (1kWh). Portable power stations are rated in Wh - a 2,000Wh station can theoretically run a 200W device for 10 hours, accounting for efficiency losses.
Is a 1000Wh power station enough for home backup?
For basic home backup covering a refrigerator, lights, router, and device charging for one day, 1,000Wh is marginal - just enough for light use. For comfortable coverage with a full refrigerator running continuously, 1,500-2,000Wh is more appropriate.
How long does a 2000Wh power station last?
A 2,000Wh station running a refrigerator (1,200Wh/day), lights (320Wh), and router (120Wh) = 1,640Wh/day total - roughly 24 hours. Adding a CPAP (240Wh/night) reduces runtime to 20 hours. With a 200W solar panel recharging during daylight, the system can sustain indefinitely.