Guide · Updated 2026-10-08

How to Size a Portable Power Station

Work out the watt-hours and output a portable power station needs by adding up your devices, with worked examples for a fridge, laptop and lights, plus losses, recharge times and safety.

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A portable power station is a large battery with sockets and an inverter. Choosing one comes down to two numbers that people often mix up: how much energy it stores (watt-hours, Wh) and how much power it can deliver at once (watts, W). Size it for both, with a margin, and it will do what you need.

Watts and watt-hours

Watts (W) measure how fast a device uses energy. A 60 W fridge draws 60 W while running.
Watt-hours (Wh) measure how much energy is used or stored. A 60 W device running for 5 hours uses 300 Wh.
A power station's capacity in Wh sets how long it runs; its output rating in W sets what it can run at the same time.

Step 1: list your devices

Write down each device, its power in watts (on the label or in the manual), how many hours you will use it, and for things that cycle on and off, such as fridges, the share of time they actually draw power (the duty cycle). Typical figures, which you should replace with your own:

Device	Typical power	Notes
Phone charging	10 to 20 W	About 15 to 20 Wh per full charge
Laptop	45 to 90 W	Check the charger rating
LED light	5 to 20 W	Very efficient
Wi-Fi router	10 to 15 W	Runs all the time
Mini fridge or small fridge-freezer	40 to 80 W	Only draws power about a third to a half of the time
TV	50 to 150 W	Depends on size
Kettle, heater or hairdryer	1,000 to 3,000 W	Drains a battery very fast

Step 2: add up the energy per day

Energy per day = watts × hours × duty cycle for each device, added together. For a power cut at home, with example figures:

Device	Watts	Hours	Duty cycle	Energy
Fridge	60	24	35%	504 Wh
Laptop	65	6	100%	390 Wh
Phone charging	15	3	100%	45 Wh
LED lights	20	5	100%	100 Wh
Wi-Fi router	12	12	100%	144 Wh
Total				1,183 Wh

Step 3: allow for losses and a reserve

A power station loses energy in its inverter, usually around 10 to 15 percent, and you should not plan to run it completely flat. Divide by an efficiency of about 0.85 and add a 20 percent reserve: 1,183 ÷ 0.85 × 1.2 = about 1,670 Wh. So you would look for a power station of around 1,700 Wh or more for this daily routine. A 1,000 Wh model would run it for only about 0.7 of a day.

Step 4: check the output rating

Add the watts of the devices you will run at once. Here, 60 + 65 + 15 + 20 + 12 = 172 W, which almost any power station can supply. Danger zone: heating and cooking appliances. A 2,000 W kettle will run a 2,000 W power station for only half an hour at most and may exceed the output limit. Motors in fridges and pumps also have a surge when they start, so check the surge rating as well as the continuous rating.

Recharging

Recharge time is roughly capacity ÷ charging power. A 1,000 Wh power station charged at 500 W from the mains takes a little over 2 hours. Charging from solar panels is slower and depends on the weather: 200 W of panels in good sun might add 800 to 1,000 Wh on a long summer day, but far less in winter or under cloud. Check the maximum solar input of the power station.

Capacity quoted vs usable

Check the usable capacity, not just the headline figure. Battery chemistry matters: lithium iron phosphate (LiFePO4) batteries tolerate deeper discharges and many charge cycles, while other types suit lighter use. Cold weather and heavy loads also reduce what you can draw.

Safety

Use it in a dry, ventilated place and keep it away from heat and water.
Do not rely on a power station for medical equipment unless the manufacturer of that equipment says it is suitable.
Power stations over about 160 Wh are not allowed on planes.
Do not charge or discharge a damaged unit, and follow the maker's instructions.

Try your own numbers

The Portable Power Station Runtime Calculator adds up your devices, allows for losses and a reserve, and shows how long a particular capacity would last. For small devices, see How Big a Power Bank Do You Need?, and to compare the running costs of mains appliances use the Appliance Running Cost Comparison.

Frequently asked questions

How long will a 500 Wh power station run a fridge? A fridge averaging about 25 W uses about 600 Wh a day, so a 500 Wh unit runs it for less than a day after losses. Check your own fridge's wattage.

Is a bigger power station always better? No. Larger units cost more and weigh more. Size for your real needs plus a reserve, and add solar panels if you need long runtimes.

Figures are examples to show the method. Always check ratings and safety guidance for the equipment you use.