Learn How to Calculate Your Portable Power Station Size

Learn How to Calculate Your Portable Power Station Size UK Guide.

By: Jonny Graham | Updated May 2026 | 10 min read time.

Buying a portable power station is a big decision. Whether you’re setting up a campervan for full-time travel, planning a weekend camping trip, preparing for emergency home backup, or building an off-grid living setup, it’s important to choose a unit that can handle your needs without breaking the bank.

A common mistake for off-grid beginners is guessing the size of the battery they need. If your power station is too small, your devices might run out of power by the second day. If it’s too big, you could spend hundreds of pounds on extra capacity you’ll never use.

The good news is you don’t need to be an electrician to figure this out. With a few numbers from your appliances and some simple maths, you can work out your power needs in just a few minutes.

This power-sizing guide will walk you through the process step by step, with real-world examples for camping, campervans, home backup, and off-grid living. By the end, you will know exactly what power station to buy for your specific situation.

Step 1: Find the Wattage of Your Appliances

Before you can figure out what size battery you need, you’ll need to know how much power each device uses. This is measured in Watts (W).

Every electrical device in the UK must show its power requirements on a sticker. You can usually find this information in three places:

• Printed directly on the “power brick” of the charging cable (like on a laptop charger).

• Stamped onto a sticker on the back or bottom of the appliance (like on a TV or travel kettle).

• Listed in the “Specifications” section of the product’s online manual.

Look for the “W”: Find a number followed by a “W” (like 65W or 1200W). If you only see Volts (V) and Amps (A), just multiply them to get the Wattage:

Volts x Amps = Watts

From the example above, a campervan 12V fridge: 12V x 5A = 60 Watts

Make a List:

Write down each appliance you plan to use with your power station, along with its Wattage. This forms the foundation of your power station capacity calculations.

Step 2: The Magic Formula (Watts x Hours)

Once you know how many Watts your appliances use, you’ll want to see how much battery they’ll use in a day. Battery capacity is measured in Watt-hours (Wh).

To figure this out, multiply the device’s Wattage by how many hours you’ll use it each day:

Watts x Hours of Use = Watt-Hours (Wh)

Here’s a quick example using the figures from the above appliances for a weekend camping trip:

In theory, a 706Wh power station would cover this daily usage. But in reality, we have to account for inefficient charging, so there’s one more important step to get the right size.

Step 3: The 85% Inverter Rule

When calculating power needs, many beginners simply add up their daily Watt-hours, buy a battery of that exact size, and then wonder why it runs out of power early. They forget about inverter inefficiency.

When your power station changes the DC power in its batteries to the 230V AC power your plugs need, some energy is lost as heat. Most good pure-sine-wave inverters are about 85% efficient.

To make sure you don’t run out of power, include this 15% loss. Take your total daily usage and divide it by 0.85:

• 706Wh (Total Daily Usage) ÷ 0.85 = 830Wh
  To run these appliances safely without draining your battery, you’ll need a power station with at least 830Wh of capacity.

Either the Bluetti AC180 or the Jackery Explorer 1000 v2 would be ideal in this scenario, at around 1000Wh capacity, each has about a 20 – 30% headroom buffer to future-proof requirements.

Step 4: Solar Replenishment (Going Off-Grid Indefinitely)

You don’t need a huge, expensive 3,000Wh power station just for a week away. You only need a battery big enough for your daily use, as long as you can recharge it the next day. Understanding solar panel sizing for your power station is key to staying off-grid long-term.

Portable power stations can be charged in a number of ways.

1. By A.C power from a wall socket (usually the fastest option).
2. 12v DC socket car cigarette lighter (the slowest charging method)
3. DC to DC alternator charger from the car battery (which charges through the solar panel input ports)
4. Solar charging (the option for off-grid)

For a complete off-grid system, solar panels are essential. If you, for instance, use 500Wh a day, you’ll need a solar setup that can generate 500Wh to recharge your battery.

In the UK summer, you can usually expect about 4 to 5 hours of strong sunlight each day.

Solar Panel Sizing Formula:

A 100W solar panel will make 400-500Wh of energy on a sunny day (100W x 5 hours.)

If you use 500Wh per day, one 100W or 200W panel can fully recharge your power station each afternoon, so you can stay off grid as long as you want.

Note: UK winters are much darker. If you live in your van all year, you’ll need the larger 200W solar panel to get enough energy on cloudy days to replenish the 500Wh of energy required.

Step 5: Putting It Together (A Real-World Example)

🎁 FREE DOWNLOAD: The Ultimate Off-Grid Power Calculator Worksheet: Stop guessing your battery needs! Download our free, printable PDF worksheet to quickly work out your daily Watt-hours, add your 85% inverter buffer, and choose the right size solar panels.

Let’s look at a real-life example. Say you’re setting up a campervan for weekend trips and want to run a small 12V fridge, charge your phones, and use some LED lights in the evening.

Here is what that maths looks like:

1. Calculate the Daily Usage:

• Campervan Compressor Fridge (45W): Fridges do not run constantly! They cycle on and off to maintain temperature. A modern 12V fridge usually runs for about 8 hours a day. (45W x 8 hours = 360Wh).
• Two Smartphones (15W each): (30W total x 2 hours = 60Wh)
• LED Cabin Lights (10W): (10W x 4 hours = 40Wh)
• Total Daily Usage 360+60+40= 460Wh
  

2. Apply the 85% Inverter Rule:

• Required capacity 460Wh ÷ 0.85 = 541Wh

3. The Final Verdict:

To safely run this setup overnight without exhausting the battery, you need a portable power station with at least 541Wh of capacity.

A 600Wh or 700Wh unit (like the Bluetti EB70 or Anker SOLIX C800) would be perfect for this setup and give you a good 20% safety buffer.

If you add a 100W or 200W portable solar panel, you could run this setup indefinitely without plugging into the mains.

Pro Tip:

While the compressor fridge draws only 45W while running, appliances with electric motors (such as fridges, pumps or fans) often require a short burst of surge power (also called starting or peak wattage) for a few seconds when they first turn on.

A typical 12V compressor fridge can momentarily surge to 2-4 times its running wattage (e.g. for this 45W fridge, it will peak at 90-180W or more for a few seconds).

Always check your power station’s surge rating (peak watts) to ensure it can handle these brief spikes without shutting down. Most 600-700Wh portable power stations have a surge rating of at least 1,000W, which is more than enough for a single 45W fridge plus charging phones or running lights at the same time.

Here is a table of commonly used appliances with the average running Watts for each.

Power Station Sizing By Use Case

Now that you know how to calculate your power needs, here’s how to choose the right power station for some common situations:

Power Station for Camping (Weekend Trips)

For a 2-3 day camping trip, you’ll usually want to power:

• LED lights (10-30W)
• Phone chargers (15-30W total)
• Small portable fridge or cooler (45-65W)
• Occasionally, a laptop or tablet

Recommended size: 600-1,000 Wh

A power station in this range will meet your basic needs for a long weekend without needing to recharge. Adding a 100-200W solar panel lets you stay out even longer, as long as you get a few hours of sunlight each day to recharge.

Best for: Festival camping, weekend wild camping, and short caravan trips.

Power Station for Campervan (Extended or Full-Time Travel)

If you live in a campervan, you’ll need to run a fridge all day, charge several devices, and power lights, fans, water pumps, and sometimes high-power items like a coffee maker or laptop.

Daily usage:

• 12V compressor fridge: 360-500Wh
• Lights and fans: 50-100Wh
• Laptops, phones, tablets: 100-200Wh
• Water pump: 20-50Wh
• Total: 530-850Wh per day

Recommended size: 1,500-2,000 Wh (or an expandable system). This size gives you enough power for a full day, plus a 20-30% buffer for cloudy days or extra use. Pair it with 200-400W of solar panels for real energy independence.

Best for: Van life, full-time travel, and long road trips in the UK or Europe.

Power Station for Home Emergency Backup

If the power goes out, you’ll want to keep your devices running:

• Wifi router and modem (20-40W), fridge (150W running, cycles on/off)
• LED lights (20-50W)
• Phone chargers (15-30W)
• Laptop (50-100W)

Typical 24Hr-usage: 500-800Wh

Recommended size: 1,500-2,000 Wh

With this capacity, you can run your essentials for 24 to 48 hours without recharging. Choose a unit with pass-through charging and UPS mode so it can automatically take over during an outage and keep your router and important devices online.

Best for: Backup power during power cuts, keeping your internet online during outages, and running medical devices like CPAP machines.

Power Station for Off-Grid Lifestyle

If you live off-grid full-time in a cabin or static caravan, your power needs are similar to a small household. You’ll likely use:

• A full-size fridge (150-200W)
• Multiple lights and fans
• Laptop and entertainment devices
• Occasional power tools or kitchen appliances

Typical daily usage: 1,000-2,000Wh

Recommended size: 2,000-3,000 Wh + 400-600W solar

For an off-grid lifestyle, use your power station with a strong solar setup. In winter, you might need a small backup generator to help during long stretches of bad weather. Using solar, battery, and a generator together gives you reliable power all year.

Best for: Off-grid cabins, permanent tiny homes, and remote workshops.

Reference Table:

Final Thoughts: Don’t Guess Your Power

Spending 10 minutes with a calculator and listing your appliance Wattages is the most important step in building your off-grid system. It saves you from dealing with a dead battery and keeps you from spending too much on a bigger unit than you need.

Remember these golden rules: Check the power stickers, multiply Watts by your daily hours of use, include that 15% inverter loss, and add a 20% safety margin to future-proof your investment.

Ready to Find Your Perfect Match?

Now that you have your “magic number” in Watt-hours, you can shop for your new system with confidence. Check out our Portable Power Station Reviews to compare the best pure-sine-wave units and find the right size for your next adventure!

Most Commonly Asked Questions