How Many Watts Do You Need? Portable Power Station Sizing Guide

Every portable power station listing throws the same two numbers at you: watt-hours (Wh) and watts (W). Get the ratio wrong and you end up with a station that either can’t run your fridge for more than twenty minutes, or one that’s twice as big (and expensive) as you actually needed. This guide walks through the math in plain terms, so you can size a station to your actual devices instead of guessing.

The two numbers that matter

• Capacity (Wh) is the size of the fuel tank — how much total energy the battery holds. A 500Wh station and a 2,000Wh station can both plug into the same outlet; the bigger one just keeps going for longer.
• Output (W) is the size of the tap — how much power it can deliver at any one instant. This is what determines whether a device will even turn on, regardless of how “full” the battery is.

A station can have huge capacity and still trip its inverter if you plug in something that draws more watts than it’s rated to output. Always check both numbers, not just the Wh figure that shows up in bold on the box.

Step 1: Add up what you actually need to run

Most devices list their wattage on a label, in the manual, or on the manufacturer’s spec page. As a rough planning reference (always confirm against your specific device):

• Small electronics: phone charger, router, LED light — usually under 30W each.
• Laptops: typically 45–100W depending on the model.
• CPAP machines: commonly in the 30–60W range.
• Mini fridge or cooler: often 50–100W running, with a brief higher surge when the compressor kicks on.
• Microwave, kettle, or space heater: these are the outliers, frequently 800–1,500W — enough on their own to demand a higher-output station.

Add up the wattage of everything you’d realistically run at the same time — not everything you own. That combined number is the minimum output rating your station needs.

Step 2: Work out how long you need it to last

Once you know your running wattage, capacity determines runtime with a simple formula:

Runtime (hours) ≈ Capacity (Wh) ÷ Load (W)

So a 1,000Wh station running a 100W load should give you roughly 10 hours (real-world numbers will be a bit lower once you account for inverter efficiency, typically 85–90%). Want to keep that same load running for a full 24-hour outage? You’re looking at closer to 2,400Wh of capacity, or a way to recharge along the way — which is where solar input becomes worth paying for.

Matching capacity to common use cases

• Phones, laptops, and lights on a weekend trip: 250–500Wh is usually plenty.
• Vanlife or remote work where you need to stay topped up for days: 500–1,000Wh, ideally paired with solar panels.
• Home backup for the essentials during an outage (router, fridge, some lighting, phone charging): 1,000–2,000Wh, or a modular system you can expand.
• Running larger appliances or backing up most of a home: multi-kilowatt systems built from expandable battery packs, often paired with a transfer switch.

Don’t forget surge watts

Anything with a compressor or motor — fridges, some power tools, air conditioners — draws a short burst well above its running wattage the moment it switches on. A fridge that runs at 100W might surge to 300–600W for a second or two. Check a station’s surge or peak rating, not just its continuous output, if you’re planning to run anything with a motor.

Why battery chemistry affects sizing too

Not all Wh are created equal over time. Stations built on LiFePO4 (LFP) cells hold their rated capacity through thousands of charge cycles, while older lithium-ion chemistries degrade noticeably faster. If you’re sizing a station for years of occasional outages rather than a single trip, it’s worth paying attention to the chemistry — a station that quietly loses 20% of its capacity in year two effectively pushed you into the next size bracket anyway.

A practical example

Say you want to keep a router (10W), a few lights (30W total), a laptop (65W), and a mini fridge (80W running, occasional 250W surge) going through an 8-hour outage. That’s roughly 185W of continuous load. Using the runtime formula: 185W × 8 hours ≈ 1,480Wh needed, so a station in the 1,500–2,000Wh range with an output rating comfortably above 250W would cover it with some margin for inefficiency.

Where this leaves you

The sizing math isn’t complicated, but it’s easy to skip and end up either underpowered or overpaying. Add up your real wattage needs, decide how many hours you need to cover, and check both the Wh and W ratings before you buy — not just the number in the ad’s headline. Brands like BLUETTI make this easier by offering a wide range of capacities with expandable battery packs, so you can start at the size you need today and add on later instead of guessing big up front.

If you’re shopping for your first unit or your third, take ten minutes with a notepad before you check out — it’s the cheapest insurance against buying the wrong size twice.