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Quick answer: add up the watt-hours (Wh) you’ll use in a day, divide by 0.85 to allow for conversion losses, and pick a power station at least that big. Then check its output in watts is higher than everything you’ll run at once. For most people that means:
- Around 250 to 300Wh: phones, laptop and lights for a day trip or a night away
- Around 1,000Wh (1kWh): a garden office, a weekend in a van with a 12V fridge, or a short power cut
- Around 2,000Wh (2kWh): longer trips off hook-up, holiday lets, or running a home fridge through a long power cut
Use the calculator below to work out your own size in a minute.
The two numbers that matter
1. Capacity (Wh): how long it lasts
Capacity is the size of the battery, measured in watt-hours. A 1,000Wh battery could, in theory, run a 100W device for 10 hours. In practice you lose around 15% converting the battery’s power to mains power, so allow for that:
Runtime in hours = capacity (Wh) x 0.85 ÷ appliance watts
2. Output (W): what it can run
Output is the most power the unit can supply at once. If you plug in more than it can handle, it switches off. This is why capacity alone isn’t enough: a large battery with a small output still can’t run a kettle.
Typical UK appliance wattages
Check the label or plug on your own kit, but these are typical figures:
| Appliance | Typical power | Will most 1kWh units run it? |
|---|---|---|
| Phone charging | 10 to 20W | Yes |
| Laptop | 45 to 90W | Yes |
| LED bulb | 5 to 10W | Yes |
| Wi-Fi router | About 10W | Yes |
| TV | 50 to 150W | Yes |
| 12V compressor fridge | 240 to 600Wh a day | Yes |
| Small microwave | About 1,100W from the socket | Yes, for short bursts |
| Hairdryer | 1,500 to 2,200W | Sometimes. Check the output |
| Electric heater | 1,000 to 3,000W | Rarely, and only briefly |
| UK kettle | 2,500 to 3,000W | No |
Worked examples
Garden office
Laptop 60W x 8 hours, monitor 25W x 8 hours, Wi-Fi 10W x 8 hours, lights 10W x 4 hours, phones 15Wh. That’s about 815Wh, so you need about 960Wh of battery: a 1kWh unit. See how to power a garden office without mains.
Weekend in a campervan
A 12V fridge (around 400Wh a day), lights (75Wh), phones (50Wh) and a laptop (180Wh) come to about 705Wh a day, so about 830Wh of battery: a 1kWh unit, or 2kWh for two days without charging. See our best power station for a campervan.
Power cut at home
A Wi-Fi router (80Wh over 8 hours), phones (30Wh), lights (50Wh) and a home fridge-freezer (roughly 1kWh a day) add up to about 1,160Wh, so about 1,365Wh of battery: a 2kWh unit to keep everything going for a full day.
Power station size calculator
Tick your kit
Tick what you’ll run and adjust the watts and hours to match your kit. Watts are on the label or plug. Figures are typical estimates.
Tips for choosing
- Round up. Batteries lose a little capacity over the years, and you’ll probably add more kit later.
- Check output as well as capacity, especially for anything with a motor or heating element.
- Think about recharging. If you can recharge every evening, a smaller unit will do. If you’ll be away for days, go bigger or add solar. Our guide to the best portable solar panels in the UK explains how much they really produce in British weather.
- Weight matters. A 1kWh unit weighs around 11 to 12.5kg, and a 2kWh unit around 17.5 to 24kg.
Frequently asked questions
What size power station do I need to run a fridge?
A 12V compressor fridge uses about 240 to 600Wh a day, so a 1kWh unit runs one for about a day or more. A home fridge-freezer uses more, so allow around 1,000Wh a day and choose a 2kWh unit for a full day of backup.
What does 1,000Wh mean?
It means the battery stores 1,000 watt-hours of energy, enough to run a 100W device for about 8.5 hours once conversion losses are taken into account.
Is a bigger power station always better?
No. Bigger units cost more and are much heavier. Buy the size you need, with a little headroom.
Can a power station run my whole house?
Not a typical UK home. Portable units are for essentials: router, fridge, lights, phones and laptops.