What Size Power Station Do You Need?
Two numbers decide it. Watts say whether an appliance will start. Watt-hours say how long it runs. Get the first wrong and nothing works; get the second wrong and it works until bedtime.
Alex Rivers
Home Improvement Editor
Last Updated
September 12, 2026
In This Guide
Almost every disappointed power station owner made the same mistake: they sized the unit against the appliances they wanted to run, and never against the hours they wanted to run them for. The inverter was never the problem. The battery was.
1. The Short Answer
For most households the honest answer is between 1,000 and 3,000 watt-hours, and where you land inside that range depends almost entirely on whether you need to get through an evening or through a night and the following morning.
The Quick Version
500Wh runs devices. 1,000Wh runs one appliance overnight. 2,000Wh runs a small household through a night. 3,000Wh and up starts to look like real backup.
Inverter output matters separately: 1,000W handles a fridge and electronics, 1,800W handles most household loads with a surge margin, and above 2,400W you are into microwaves, kettles and power tools.
The rest of this guide is how to arrive at your own number rather than borrowing someone else's. It takes about ten minutes and a look at the labels on the back of two or three appliances.
2. The Two Numbers That Matter
Every power station is sold with two headline figures, and they answer completely different questions.
- Watts (W) is the inverter's output — the rate of power it can supply. It sets what you can run at once. Exceed it and the unit shuts the outlet off; it does not run slowly or struggle.
- Watt-hours (Wh) is the battery's capacity — the total quantity of energy stored. It sets how long you can run things. A 1,000Wh pack supplies 100 watts for ten hours, or 500 watts for two.
A useful analogy: watts are the width of the pipe and watt-hours are the size of the tank. A wide pipe on a small tank empties fast. A narrow pipe on a big tank cannot fill a bath quickly no matter how long you wait. You need both to be right, and manufacturers love to advertise whichever one flatters the product.
There is a third figure worth finding, usually buried in the specification table: surge or peak watts. Anything with a motor — a fridge compressor, a sump pump, a power tool — draws several times its running wattage for a fraction of a second on startup. The surge rating says whether the unit can absorb that spike.
3. Step One: Add Up Your Peak Watts
List everything that might be running simultaneously at the worst moment, and add the running watts together. Then add the single largest starting surge on the list, not all of them, because the odds of two compressors starting in the same half-second are small enough to ignore.
| Appliance | Running Watts | Starting Surge |
|---|---|---|
| Full-size refrigerator | 100–200W | 600–1,200W |
| Chest freezer | 80–150W | 500–1,000W |
| Gas furnace blower | 300–800W | 900–2,400W |
| Sump pump (1/3 hp) | 600–800W | 1,800–2,400W |
| CPAP, no humidifier | 30–60W | None |
| Router and modem | 10–25W | None |
| LED lamps (six) | 40–60W | None |
| Microwave (1,000W rated) | 1,400–1,700W | Brief, similar |
| Coffee maker or kettle | 900–1,500W | None |
| Space heater | 750–1,500W | None |
Note the microwave row, because it surprises nearly everyone. A microwave advertised as 1,000 watts is describing its cooking output, not its electrical draw; the real consumption is closer to 1,500 watts. The same trap applies to some pressure washers and vacuum cleaners. Our wattage chart lists more appliances, and the figures work identically for batteries.
One more caution on surges. Some power stations advertise a boost mode that runs higher-wattage appliances by slightly reducing the output voltage. It genuinely works on resistive loads such as heaters, kettles and hair dryers, and it does not work on anything with a motor or a compressor. Never size a fridge or a pump around a boost figure.
4. Step Two: Add Up Your Daily Watt-Hours
This is the step almost everybody skips, and it is the one that decides whether you are still watching television at midnight. Multiply each appliance's running watts by the hours it will actually be drawing power — not the hours it is switched on, which is a different and much larger number.
The distinction matters most for anything thermostatically controlled. A refrigerator is plugged in for twenty-four hours but its compressor runs for perhaps eight of them, so a 150W fridge consumes around 1,200Wh a day rather than 3,600Wh. A furnace blower on a cold night might run a third of the time. A CPAP, by contrast, runs continuously for every hour you are asleep.
| Load | Duty Cycle | Energy per 24h |
|---|---|---|
| Refrigerator | 30–40% | 1,000–2,000Wh |
| Chest freezer | 25–35% | 700–1,200Wh |
| Furnace blower, cold night | 30–50% | 1,000–2,500Wh |
| CPAP, eight hours | 100% | 250–500Wh |
| Router, phones, laptop, lights | Mixed | 300–500Wh |
| Sump pump, wet basement | 5–20% | 800–3,000Wh |
Add the rows that apply to you and you have your daily figure. Most households arrive somewhere between three and six kilowatt-hours for genuine backup, which is a sobering number the first time you see it against a 1,000Wh unit — and exactly why the honest advice is often to pair a battery with an engine, as we set out in power station versus generator.
5. Rated Capacity Is Not Usable Capacity
The watt-hour figure on the box describes the energy in the cells, not the energy that reaches your appliances. Three things stand between the two, and together they cost more than most buyers expect.
The inverter is the largest loss. Converting direct current from the battery into household alternating current runs at roughly eighty-five to ninety-two per cent efficiency in good units, and worse at very light loads, where the inverter's own overhead becomes significant relative to what it is delivering. Running a 5W phone charger through a 2,000W inverter is a genuinely wasteful way to use a battery; the DC and USB outputs bypass the inverter entirely and are noticeably more efficient.
The battery management system is the second. It reserves a slice of capacity at both ends of the range to protect cell life, so a pack advertised at 1,000Wh may only cycle through perhaps 950Wh of that. Cold is the third: lithium chemistry delivers less capacity below about 5°C, and lithium iron phosphate packs will refuse to charge at all below freezing without an internal heater.
Plan On This
Assume eighty-five per cent of the rated watt-hours reach your AC outlets at room temperature.
A 1,000Wh unit is an 850Wh unit in practice, and closer to 700Wh in a cold garage in February. Size against the honest number, not the marketing one.
6. Sizes by Scenario
With the arithmetic done, the categories sort themselves out cleanly.
| Capacity | Inverter | What It Is Actually For |
|---|---|---|
| 200–500Wh | 300–600W | Phones, laptops, camping lights, a CPAP for a night |
| 500–1,000Wh | 600–1,200W | A fridge overnight, or an evening outage's essentials |
| 1,000–2,000Wh | 1,500–2,000W | Fridge, internet, lights and a furnace blower for a night |
| 2,000–3,500Wh | 2,000–3,600W | A full day of household essentials, kettle and microwave included |
| 3,500Wh and up | 3,000W+ | Multi-day backup, usually with solar and expansion packs |
Weight is the quiet constraint on that table. Capacity and mass climb together, and a 2,000Wh unit typically weighs between forty and sixty pounds. Above about 3,000Wh you are buying furniture with wheels rather than something you will carry to a campsite, and it is worth being honest about which of those you actually want.
7. Three Worked Examples
The suburban evening outage. A refrigerator, the router, four LED lamps and phone charging, for eight hours until power returns. Peak watts: 200 running plus a 1,000W compressor surge, so a 1,000W inverter suffices. Energy: about 500Wh for the fridge over eight hours, plus 150Wh for everything else. Total around 650Wh, which after inverter losses means a 1,000Wh unit is right and a 500Wh unit is not.
The cold-climate winter night. Furnace blower, refrigerator, internet and lights, from six in the evening until nine the next morning. Peak watts: the blower's 2,000W startup surge sets the requirement, so an 1,800W continuous inverter with a 3,000W surge rating is the minimum. Energy: roughly 1,500Wh for the blower, 900Wh for the fridge and 250Wh for everything else — about 2,650Wh, so a 3,000Wh unit or a 2,000Wh unit plus an expansion battery.
The medical priority. A CPAP with the heated humidifier turned off, plus phone charging, for three nights. Peak watts: under 100, so even a small inverter works. Energy: about 350Wh a night, so roughly 1,050Wh over three nights. A 1,500Wh unit covers it with margin, and running the CPAP from the DC output rather than the AC outlet stretches it further — see our CPAP guide for how much that saves.
Notice that the middle example needs four times the capacity of the first, and that the difference is heating rather than anything glamorous. Heat is always the expensive load, whether it is a furnace blower moving warm air or a space heater making it.
8. Expansion, Recharging and Buying for Later
Two features change the sizing calculation more than any amount of extra capacity, and both are worth paying for if your outages might run long.
The first is expandability. Many mid-size and large units accept add-on battery packs that connect to the same inverter, letting you double or triple stored energy without buying a second inverter you do not need. If you are torn between two sizes, an expandable smaller unit is usually the better purchase — as long as you check that the expansion battery is currently sold rather than merely promised.
The second is solar input. A battery that can be refilled during the day stops being a fixed budget and starts being a daily allowance, and that transforms what a modest unit can do across a multi-day outage. The specification to look for is the maximum solar input in watts and the acceptable voltage range; our guide to charging with solar covers what those numbers mean in real sunlight, which is a good deal less generous than the panel ratings suggest.
Also check AC recharge speed, which varies enormously between models. Some units refill from empty to eighty per cent in under an hour; others take six. In a rolling outage, or when you have a generator running for a couple of hours a day, that difference decides how much energy you can actually bank. Once you have your number, our tested power station picks break down which units deliver on it.
When the Answer Is Not a Power Station
Sizing exercises sometimes produce a number that no battery can reasonably meet, and it is worth recognising that outcome rather than buying up the range in hope. If your list includes central air conditioning, an electric water heater, an electric range or a whole-house well pump, the daily energy figure will land in the tens of kilowatt-hours and the honest conclusion is that you need an engine.
That does not mean the battery has no place. Many households size a power station for the loads that must never be interrupted and a generator for everything else, which is cheaper than sizing either one to do the whole job alone. Our guides to generator sizing and whole-house wattage pick up where the battery arithmetic stops.
The reverse case is also common and much happier. Plenty of people work through this exercise expecting to need a generator and discover that their genuine must-run list is a fridge, a router and a phone charger — perhaps 800Wh over an evening. That is a modest, silent, maintenance-free purchase, and it will sit in a cupboard doing nothing for a year without any of the fuel and carburettor problems an engine brings.
9. Common Mistakes to Avoid
Sizing on Watts and Ignoring Watt-Hours
A 2,000W inverter on a 500Wh battery will start almost anything in your house and then run it for fifteen minutes. Inverter output is the easy specification to satisfy; capacity is the one that decides whether the unit is still working at midnight.
Forgetting Starting Surge on Motors
A fridge that runs at 150 watts can demand 1,000 for a fraction of a second when the compressor kicks in. Size the inverter against the surge, not the running figure, or the unit will trip every time the appliance cycles — usually at three in the morning.
Using Rated Capacity in the Arithmetic
Inverter losses and management reserves take roughly fifteen per cent before your appliances see any of it, and cold weather takes more. Run your numbers against eighty-five per cent of the printed figure and the result will match reality.
Counting Hours Switched On Instead of Hours Drawing Power
A refrigerator is plugged in for twenty-four hours but only draws power for eight of them. Sizing on connected hours produces a number three times too large and pushes people toward equipment they neither need nor can lift.
Assuming Boost Mode Solves Surge Problems
Voltage-reducing boost features genuinely run high-wattage resistive loads such as kettles and heaters, but they do nothing for motors and compressors. Never size a fridge, pump or power tool around a boost rating.
10. Frequently Asked Questions
What size portable power station do I need for home backup?
For a fridge, internet, phones and lights through an evening outage, 1,000 to 1,500Wh. To carry those plus a gas furnace blower through a full night and into the morning, 2,000 to 3,000Wh. Below 500Wh you are powering devices rather than a household.
How many watt-hours do I need per day?
Add the daily consumption of what you intend to run. A full-size fridge uses 1,000 to 2,000Wh, a furnace blower 1,000 to 2,500Wh on a cold night, and phones, router, laptop and lights around 400Wh together. Three to six kilowatt-hours is a realistic backup day.
Is 1,000Wh enough for a power station?
It is enough for a fridge overnight, a CPAP for two or three nights, or a camping weekend of phones, lights and laptops. It is not enough to carry a household through a full day. Think of 1,000Wh as one appliance for one night.
Do I need more watts or more watt-hours?
Watts decide whether an appliance starts at all; watt-hours decide how long it runs. Check watts first, since an undersized inverter simply refuses the load, then check capacity against your daily total. Most buyers get the watts right and the watt-hours wrong.
How much usable capacity does a power station actually have?
Plan on about eighty-five per cent of the rated figure through the AC outlets. The inverter loses ten to fifteen per cent converting DC to AC and the management system holds a reserve, so a 1,000Wh unit delivers roughly 850Wh — and less in the cold.
What size power station runs a refrigerator?
Any unit with a 1,000W or larger inverter will start a domestic fridge, and 1,000Wh runs one for eight to fourteen hours. For a full twenty-four hours of fridge and freezer, size at 2,000Wh, because the compressor's duty cycle climbs as the kitchen warms.
Should I buy a bigger power station than I need?
One size larger than the arithmetic suggests, but not three. Cold, ageing cells and inverter losses all erode real capacity, and a pack that is never fully drained lasts longer. Past that, extra capacity buys weight you will not carry and money better spent on panels.
Can I expand a portable power station later?
Many mid-size and large models accept add-on packs that double or triple capacity on the same inverter. Buying into an expandable range beats replacing the whole unit later — but confirm the expansion battery is actually on sale before relying on the promise.
Related Backup Power Guides
The Bottom Line
Size on two numbers, in order. Add the running watts of everything that might be on at once, add the largest single starting surge, and buy an inverter that clears the total. Then add the watt-hours those same appliances consume across the hours you need them, and buy a battery that clears that figure with fifteen per cent to spare for conversion losses.
For most households the answer lands between 1,000 and 3,000 watt-hours with an inverter between 1,500 and 2,400 watts. Evening outages and a fridge sit at the bottom of that range; a winter night with a furnace blower sits at the top.
If the arithmetic produces a number no battery can meet, that is a useful result rather than a failed exercise. It means your requirement is an engine, or a battery for the loads that must never blink and an engine for everything else.
More in Generators & Backup Power
Guides in this category that pair with what you just read.
About the Author
Alex Rivers, Home Improvement Editor
Alex has spent over a decade working on residential and light commercial property maintenance, and now tests every tool, coating and machine that appears in these guides personally.