Power Runtime Calculator
Estimate the battery capacity and inverter output you need for refrigerators, lights, electronics, medical devices, camping equipment and emergency backup. Enter appliance wattage, quantity and runtime to calculate a practical portable power station size.
Choosing a portable power station by watt-hours alone can lead to disappointing runtime or an inverter that cannot start your appliances. This calculator estimates both the battery capacity and output rating you need, then adds a practical safety margin for inverter losses, battery limits and unexpected loads.
Size for Both Watt-Hours and Maximum Watts
Your power station must have enough battery capacity for the total energy you plan to use and enough inverter output for the highest simultaneous load. For most buyers, adding a 20% to 30% reserve produces a more realistic result than sizing exactly to the calculated minimum.
Power Runtime Calculator
Add each device you plan to run. Use the appliance's running watts and the number of hours it will operate between charges.
Estimate Battery Runtime
Enter up to six appliances or devices. Leave unused rows blank.
Raw appliance energy before losses and reserve.
Battery capacity after efficiency and reserve allowances.
Estimated simultaneous running load.
Includes the larger of running load plus margin or surge requirement.
Estimated runtime class: Large 2,000–3,000Wh portable power station with at least a 1,200W inverter.
Understanding Your Calculator Results
Total Energy Use
The raw watt-hours required by all devices before allowing for inverter losses or reserve capacity.
Recommended Capacity
The minimum battery size after adding the selected efficiency and reserve allowances.
Recommended Inverter
The output rating needed to handle simultaneous running loads and the highest estimated startup surge.
How the Portable Power Station Sizing Formula Works
Runtime depends on usable battery capacity and appliance power draw. Multiply each device's running watts by the number of units and the hours of operation, then add every device together.
Runtime Formula
Estimated Runtime (hours) = Battery Watt-hours × Efficiency ÷ Appliance Watts
After calculating the raw total, the calculator adds efficiency losses and reserve capacity. These allowances compensate for inverter conversion, internal electronics, temperature, aging and real-world variation.
Inverter output is measured in watts rather than watt-hours. The inverter must support the combined running load of devices used at the same time and the brief startup surge of motors or compressors.
Common Portable Power Station Size Examples
| Use Case | Typical Capacity Range | Typical Inverter Range |
|---|---|---|
| Phones, tablets and lights | 300–500Wh | 300–600W |
| Camping electronics and small fridge | 500–1,000Wh | 600–1,200W |
| Refrigerator, router and emergency lighting | 1,000–2,000Wh | 1,200–2,000W |
| RV appliances and longer off-grid use | 2,000–4,000Wh | 2,000–3,600W |
| Multi-appliance home backup | 3,000Wh and above | 3,000W and above |
Do Not Ignore Starting Watts
Refrigerators, freezers, pumps, air conditioners and power tools may require several times their normal running wattage for a brief moment when the motor starts. A power station can have enough battery capacity but still shut down if its inverter cannot supply that surge.
Mostly Electronic Loads
Laptops, phones, routers and LED lights usually have low startup demands. A modest inverter margin is often sufficient.
Motor and Compressor Loads
Refrigerators, pumps and air conditioners require careful surge planning. Use the appliance label or manufacturer specifications whenever possible.
Why Real Runtime Is Lower Than Advertised Capacity
A 1,000Wh power station does not normally deliver a full 1,000Wh through its AC outlets. Energy is lost through the inverter, cooling system, internal electronics and battery protection limits.
Real usable capacity may be approximately 75% to 90% of the advertised rating depending on load type, temperature and product design. High-power AC appliances typically produce more loss than small DC loads.
Portable Power Station Buying Checklist
Calculate Watt-Hours
Add the energy required by every appliance between charges.
Check Continuous Output
Make sure the inverter supports everything that may run at the same time.
Check Startup Surge
Confirm that refrigerators, pumps and tools can start without overloading the inverter.
Plan Recharging
Compare AC, vehicle and solar charging speeds with your expected usage.
Choose Battery Chemistry
LiFePO4 batteries are usually preferred for frequent cycling and long-term ownership.
Leave Extra Capacity
Round up for future devices, colder conditions and battery aging.
Final Sizing Recommendation
Choose a portable power station that exceeds both your calculated battery requirement and your highest expected wattage. For emergency backup, a 20% efficiency allowance plus a 20% reserve is a practical starting point.
When two models meet the result, the larger unit usually provides better flexibility, longer runtime and less stress on the battery.
Frequently Asked Questions
How many watt-hours do I need in a portable power station?
Multiply each device's watts by its hours of use, add the totals, then add allowances for efficiency losses and reserve capacity.
Is a 1,000Wh power station enough for a refrigerator?
It may be enough for several hours, but runtime depends on the refrigerator's average consumption and startup surge. Confirm both capacity and inverter output.
What size power station do I need for camping?
Small camping setups may need 300–500Wh, while refrigeration, laptops and multiple-day trips often require 500–1,500Wh or more.
How much reserve capacity should I add?
A 20% reserve is a reasonable minimum. Add more for emergency use, cold weather, battery aging or uncertain appliance consumption.
What is the difference between watts and watt-hours?
Watts measure how much power an appliance uses at one moment. Watt-hours measure how much total energy the battery can supply over time.
Does solar charging reduce the battery size I need?
Solar can extend runtime, but weather and charging limits are unpredictable. The battery should still cover essential overnight or low-sun periods.
Why does my power station run for less time than the calculation suggests?
Inverter losses, temperature, device cycling, battery protection and inaccurate appliance ratings can all reduce actual runtime.
Should I buy a larger power station than the calculator recommends?
Usually yes. Rounding up provides a safety margin and gives you more flexibility for additional devices or longer outages.
Calculator results are estimates. Always confirm appliance wattage, startup surge and manufacturer specifications before relying on a power station for critical equipment.