Portable Power Station Size Calculator: Find the Watts and Watt-Hours You Need
Estimate the battery capacity and continuous AC output required for your actual appliances. Use the calculator, check the worked examples, and account for inverter losses before buying.
This page uses transparent electrical arithmetic, not measured product runtime tests. The default 85% usable-energy factor is an illustrative AC efficiency allowance, not a guarantee for any station. Idle draw, temperature, aging, battery reserve, load shape and manufacturer operating limits can change results.
Size for Peak Watts and Total Watt-Hours Separately
First add the watts of appliances you plan to run at the same time to determine required continuous AC output. Then multiply each appliance's average running watts by hours of use, add the watt-hours, and divide by your estimated usable-energy fraction to find a minimum nominal battery capacity.
Example: a 60W laptop for 5 hours plus a 10W router for 8 hours needs 380Wh at the devices. At an illustrative 85% delivery factor, that is 447Wh of nominal battery capacity before extra reserve.
Portable Power Station Size Calculator
Enter up to five appliance loads. Use each device's measured average running wattage where possible, not a guessed maximum. For intermittent appliances such as a refrigerator, use an appropriate duty-cycle-adjusted average for energy planning while still checking its startup surge separately.
| Appliance | Average watts | Hours used | Energy (Wh) |
|---|---|---|---|
| 300 | |||
| 80 | |||
| 60 | |||
| 24 | |||
| 0 |
Daily device energy: 464 Wh
Minimum nominal battery before reserve: 546 Wh
Suggested nominal battery including reserve: 655 Wh
Continuous AC output planning target (25% headroom): 107 W
Check motor startup surge, individual outlet ratings, and station operating limits separately.
Important: The simultaneous-load field is separate because the appliance list may include devices used at different times. Do not add all appliance wattages unless you actually intend to operate them together. This calculator estimates one day's usage; multiply daily Wh by the number of days between recharges for a multi-day plan.
Worked Sizing Examples
| Use case | Device energy | Nominal capacity at 85% | With 20% reserve |
|---|---|---|---|
| Laptop 60W x 5h + router 10W x 8h | 380Wh | 447Wh | 537Wh |
| CPAP 40W x 8h (no humidifier assumed) | 320Wh | 377Wh | 452Wh |
| Fan 45W x 10h + 3 LED lamps 8W each x 5h | 570Wh | 671Wh | 805Wh |
| TV 100W x 4h + router 12W x 6h | 472Wh | 556Wh | 667Wh |
| Small cooler averaging 35W x 24h | 840Wh | 989Wh | 1,186Wh |
These examples are illustrative, not guaranteed appliance ratings. A CPAP's humidifier and heated tubing may change demand substantially. Compressor coolers have variable duty cycles and startup loads; use measured energy where available.
Three Checks Before Choosing a Station
Continuous AC watts
A station must supply the sum of the devices that will run simultaneously. A 1,000Wh battery with a 300W inverter cannot run a 900W appliance, even though it has substantial stored energy.
Battery watt-hours
Watt-hours estimate how long equipment can operate. A 500Wh battery does not provide 500Wh of guaranteed usable AC energy after conversion losses and reserve.
Startup and surge
Compressors, pumps and motors can briefly draw more than their running watts. Verify the station's surge capability, duration and manufacturer guidance before purchase.
Which Battery Capacity Class Fits Your Use?
| Nominal capacity class | Typical planning fit | Watch for |
|---|---|---|
| 300-500Wh | Phones, routers, low-watt laptops, short outages | Limited runtime for AC appliances; inverter output varies |
| 500-1,000Wh | Remote work, small electronics, brief overnight essentials | Confirm CPAP settings and actual AC draw |
| 1,000-2,000Wh | Multiple electronics, longer essential-load backup | Check output for kettles, microwaves and motors |
| 2,000Wh and above | Higher energy budgets and longer backup windows | Weight, recharge time, expansion and circuit compatibility |
These are planning categories, not performance claims about particular models. A large battery does not imply a high enough inverter rating for every appliance, and high AC wattage does not imply long runtime.
300-500Wh Options
Useful when the measured energy budget is small and easy portability matters most.
1,000Wh-Class Options
Compare rated inverter output, usable capacity, charging input and warranty.
2,000Wh-Class Options
Consider recharge logistics, appliance compatibility, storage and portability.
Common Sizing Mistakes That Lead to Disappointment
- Using surge watts as continuous watts. A temporary surge specification is not a sustained output rating.
- Assuming nameplate battery Wh is fully available at the AC socket. Conversion and standby losses reduce delivered energy.
- Ignoring simultaneous operation. A coffee maker and microwave used together may exceed the inverter even if each works alone.
- Guessing refrigerator energy from compressor running watts. Duty cycle varies with ambient temperature, door openings and food load.
- Confusing USB and AC charging efficiency. Direct DC/USB delivery may have different losses from an AC inverter.
- Planning multiple days without multiplying energy needs. Two days without recharge approximately doubles the required device Wh.
- Using indoor combustion generators as a substitute. Fuel generators create carbon monoxide hazards and must never be operated indoors or in enclosed spaces.
For medical equipment, do not rely on an illustrative calculator alone. Verify actual draw and startup behavior, and maintain an appropriate manufacturer- or clinician-approved backup plan.
Final Verdict: Calculate Energy, Then Check Output
Start with a measured or documented appliance energy budget. Divide total device watt-hours by a realistic usable-energy allowance, then add reserve for uncertainty and battery aging. Separately confirm the inverter's continuous AC watt rating and the starting surge of motor-driven equipment. A station that passes only one of these checks is not correctly sized.
The calculator is a screening tool, not a certification of appliance compatibility or measured runtime. Check the exact station manual before connecting critical loads.
Frequently Asked Questions
What size power station do I need for a refrigerator?
Measure or obtain the refrigerator's daily kWh use and verify compressor startup surge. The battery must cover the daily energy requirement after losses, and the inverter must handle the startup demand.
Is a 1,000Wh power station the same as 1,000W?
No. 1,000Wh is stored energy; 1,000W is a rate of power delivery. A station can have a 1,000Wh battery and a different continuous inverter rating.
How long will a 500Wh power station run a 100W appliance?
At an illustrative 85% usable-energy factor, about 4.25 hours (500 x 0.85 / 100). Actual results vary with idle draw, temperature and the station.
Should I add every device wattage together?
Only add devices that will operate at the same time for continuous inverter sizing. Add each device's watt-hours across the planned period for battery sizing.
How much extra battery capacity should I allow?
The calculator defaults to 20% reserve after an 85% usable-energy assumption. Those are adjustable planning inputs, not universal requirements.
Does a solar panel reduce the required battery size?
Solar input can replenish energy, but output depends on weather, angle, shading and charge limits. Size essential overnight loads without assuming reliable sunshine.
Can this calculator guarantee CPAP or medical-device runtime?
No. Heated humidifiers, tubing and pressure settings affect consumption. Use the device manufacturer's guidance, measured draw and an appropriate backup plan.
Sources and Editorial Methodology
The calculations follow the electrical relationship energy (Wh) = power (W) x time (hours). The 85% usable-energy and 20% reserve defaults are transparent editorial assumptions, not manufacturer-verified efficiency figures. All appliance wattages and duty-cycle examples are illustrative; no hands-on testing or real-time prices are claimed.