Solar and Power Station Calculator
Add each device with its watts and hours of use per day. The calculator totals your daily watt-hours, adds a margin for inverter losses and tells you the capacity and output to look for. Then use the result to pick a size class and a matching solar panel.
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This calculator tells you how much battery capacity, inverter output and solar power you need. Add the devices you want to run, how many watts each uses and for how many hours a day. It does the math below and gives you sizes to shop for.
| Device | W | Hours/day | Wh |
|---|---|---|---|
| Phone (charging) | 0 | ||
| Laptop | 0 | ||
| 12V compressor fridge | 0 | ||
| LED lights | 0 | ||
| CPAP (no humidifier) | 0 | ||
| Wi-Fi router | 0 | ||
| 32" TV | 0 | ||
| Electric kettle | 0 |
Daily use: 0 Wh · Peak draw: 0 W
Recommended capacity (×1.25 for inverter losses and reserve): 0 Wh
Panel to refill it in a day (4 peak sun hours, 75% real-world yield): 0 W
How does the calculator work?
It applies three simple formulas, the same ones we use in our reviews.
- Daily energy: Σ(watts × hours) for every device, in Wh.
- Capacity to look for: daily Wh ÷ 0.85, to cover inverter and conversion losses.
- Output to look for: the sum of the watts of devices running at the same time, plus a margin of about 20%.
To size solar, divide the daily Wh by peak sun hours × 0.75. Our guide on how many solar watts you need explains peak sun hours by US region.
How do I read the result?
Treat the capacity figure as a minimum and the output figure as a must-have. If a station’s continuous output is below your simultaneous load, it will shut off. If the capacity is below your daily need, it will run out early.
Example: a CPAP (40 W × 8 h) and a laptop (60 W × 3 h) use 500 Wh. Add LED lights (10 W × 5 h) and two phones (10 W × 2 h), and the total is 570 Wh. Divided by 0.85, that is 671 Wh of capacity. Peak simultaneous load is about 120 W, so almost any station has enough output.
Also check the surge rating if you run motors. Fridges, pumps and air conditioners need a short startup spike above their running watts.
What should I buy based on my result?
Pick the size class that covers your capacity result, then compare models within it.
| Your result | What it usually means | Where to look |
|---|---|---|
| Under 700 Wh | CPAP, laptops and lights for a night | Best for RV and van camping |
| 700–1,300 Wh | Weekend camping, short outages | Best portable power stations |
| 1,300–2,500 Wh | A day of home essentials | Best for home backup |
| Over 2,500 Wh | Multi-day backup; plan for solar | Best solar generators |
If you want to recharge from the sun, add panels sized with the formula above. Our best portable solar panels compare options by efficiency, weight and connector.
Which mistakes skew the result?
Three errors cause most bad estimates.
- Using label maximums for fridges: the label shows peak draw; the average is much lower.
- Forgetting standby loads: routers, modems and TVs on standby run all day.
- Ignoring startup surge: motors need several times their running watts for a moment.
What are typical appliance watts?
These are common averages; your devices may differ. Measure with a plug-in watt meter for the best result.
- Wi-Fi router and modem: about 15 W.
- LED light bulb: about 10 W.
- CPAP without humidifier: about 40 W.
- Laptop: about 60 W.
- Full-size fridge: about 60 W on average.
- 12V compressor cooler: about 45 W on average.
- Microwave: about 1,200 W while running.
- Space heater: about 1,500 W.
For a step-by-step walkthrough of every spec, read how to choose a portable power station.
Frequently asked questions
How do I find the watts of my appliance?
Check the label on the device or its power adapter. If it lists volts and amps instead, multiply them: at 120 V, a 2 A device uses about 240 W.
Why does the calculator add a margin to my total?
The inverter and electronics in a power station lose about 10–15% of the energy. Dividing by 0.85 makes sure the battery still covers your needs after those losses.
What should I enter for a refrigerator?
Use the average draw, not the label maximum, and 24 hours. A typical modern full-size fridge averages around 60 W; the startup surge is much higher, so check the station’s surge rating too.
How accurate is the result?
It is as accurate as the numbers you enter. Measuring your devices with a plug-in watt meter gives the best results.