Backup Power Basics: Watts vs Watt-Hours and Why It Matters

Published: January 19, 2026Last updated: January 24, 2026Reading time: 16 minTopic: Blackouts & Backup Power

When the power goes out, most people care about two things: what they can still run, and for how long. Those two questions come down to understanding watts (W) and watt-hours (Wh). Knowing the difference helps you avoid disappointment, choose realistic backup power options, and stretch what you already have.

This is not about building a complex off-grid system. It is about calm, practical decisions for short-term outages in typical homes and apartments in the United States. With a few simple ideas, you can estimate whether a small battery pack, a power station, or a portable inverter can keep essentials like phones, a router, a lamp, or a medical device running long enough to be useful.

Watts tell you how much power something uses at a moment in time. Watt-hours tell you how much energy is stored or consumed over time. Both numbers show up on backup power gear and home appliances, and mixing them up is one of the most common sources of confusion.

Why Watts and Watt-Hours Matter for Home Blackouts

Watts vs Watt-Hours: The Core Concepts

Watts and watt-hours sound similar, but they answer different questions:

Watts (W): How fast energy is being used or delivered right now. Think of this as the size of the “pipe.”
Watt-hours (Wh): How much total energy is used or stored over time. Think of this as how much “water” is in the tank.

A simple way to connect them is:

Power (W) × Time (hours) = Energy (Wh)

Some practical examples using approximate, everyday numbers:

A small LED lamp might use about 5 watts.
A Wi‑Fi router might use around 10–15 watts.
A laptop might use 30–60 watts while charging.
A refrigerator may average 80–150 watts over time but have short higher spikes when it starts up.

If you run a 10-watt device for 5 hours, it uses 50 watt-hours (Wh) of energy. If you have a battery that stores 200 Wh, in a perfect world it could run that 10-watt device for about 20 hours (200 Wh ÷ 10 W). In reality, you will get less because of losses and inefficiencies, but the math gives a good ballpark.

When you look at backup power gear:

Maximum watts (W) tells you what devices it can power at all.
Capacity in watt-hours (Wh) tells you how long it can run them.

Table 1. Choosing backup power by focusing on watts vs watt-hours. Example values for illustration.

Situation	What matters more?	Why it matters	Planning note
Charging phones and small devices only	Watt-hours (Wh)	Most small devices use low watts but may need many hours	Look for enough Wh to cover several charge cycles
Running a laptop and home internet	Both W and Wh	You need enough watts to power both at once and enough Wh for work time	Add up watts of each device and multiply by desired hours
Powering a few LED lamps in the evening	Watt-hours (Wh)	Lamps use low wattage but you may run them many hours	Estimate daily Wh use for typical outage evenings
Running a refrigerator during a long outage	Watts (W) first	You must cover starting surge watts, then consider total daily energy	Check both running watts and an allowance for startup spikes
Powering power tools briefly after a storm	Watts (W)	Tools may draw high watts but for short periods	Ensure the backup source can handle the tool’s peak watt draw
Keeping a small fan on during a heatwave outage	Watt-hours (Wh)	Fans run at modest watts but may need many hours daily	Multiply fan watts by planned hours per day

How to Read Device and Backup Power Labels

Most home devices and backup power gear have some information printed on a label or in a basic information sheet. Learning where to look makes it much easier to plan.

Finding Watts on Common Household Devices

You can usually find watts (W) or volts (V) and amps (A) on a sticker, plate, or small print near the cord or plug. If you see volts and amps instead of watts, you can estimate watts with:

Watts ≈ Volts × Amps

In most U.S. homes, standard outlets are about 120 volts. Some typical examples (numbers are approximate):

Phone charger: 5–20 W while charging
Wi‑Fi router: 10–20 W
LED table lamp: 5–10 W
Floor fan: 40–70 W on low to medium settings
Mini fridge: 50–100 W average, higher for short bursts

These numbers are only starting points. Actual devices may use more or less, but thinking in ranges helps you avoid huge misjudgments, like assuming a refrigerator uses the same power as a phone charger.

Understanding Backup Battery and Power Station Specs

Most consumer backup power gear lists at least two important numbers:

Capacity – often in watt-hours (Wh) or sometimes amp-hours (Ah). For planning, Wh is easier.
Output power – usually in watts (W), with a continuous rating and sometimes a brief surge rating.

If capacity is given in amp-hours, you can estimate watt-hours with:

Watt-hours ≈ Volts × Amp-hours

For example, a 12-volt, 50 amp-hour battery would hold about 600 watt-hours (12 V × 50 Ah). Real usable capacity will be less, especially for some battery types that should not be drained fully.

Key ideas when comparing options:

Continuous watts tell you how much load you can run steadily.
Surge watts matter for devices with motors, such as refrigerators or some fans.
Total watt-hours give a rough idea of runtime, once you know the loads.

Estimating Runtime: Simple Step-by-Step Examples

You do not need exact laboratory numbers to make useful decisions. Reasonable estimates are enough to decide which devices you will prioritize and whether a given backup setup is worth the cost and space in your home.

Step 1: List Devices You Want to Power

Start by deciding what really matters during a typical short outage in your situation. For many homes and apartments, a practical list might include:

Phones and a basic way to charge them
Internet modem and router, if your service still works in an outage
One or two LED lamps or string lights
A small fan in hot weather, or an electric blanket pad in cold weather (if feasible with your system)
Recharging batteries for flashlights or radios

Families with seniors, infants, or medical equipment may have additional priorities. For any device that affects safety or basic comfort, check its power label carefully.

Step 2: Estimate Watts for Each Device

Write down the approximate wattage for each device. If you cannot find a label, use a reasonable range from similar devices. For example:

Phone charger: 10 W
Wi‑Fi router: 15 W
Laptop: 50 W
LED lamp: 8 W
Small fan: 50 W

Add up the watts of all the devices you plan to run at the same time. This total must be below the continuous watt rating of your backup power source.

Step 3: Estimate Hours of Use

Next, decide how many hours per day you want to run each device. For example, in a summer evening outage:

Phone charging: 2 hours total
Wi‑Fi router: 4 hours
Laptop: 3 hours
LED lamp: 5 hours
Small fan: 4 hours

Now convert each one to watt-hours:

Phone charger: 10 W × 2 h = 20 Wh
Wi‑Fi router: 15 W × 4 h = 60 Wh
Laptop: 50 W × 3 h = 150 Wh
LED lamp: 8 W × 5 h = 40 Wh
Small fan: 50 W × 4 h = 200 Wh

Total energy for that day: 20 + 60 + 150 + 40 + 200 = 470 Wh.

Step 4: Compare to Your Backup Power Capacity

If your battery or power station is rated at 500 Wh, you might think it could cover about 470 Wh. But it is sensible to assume some loss:

Inverter losses converting battery power to household AC
Battery chemistry limits (some types should not be fully drained)
Variations in actual device wattage

A common rule of thumb is to expect around 60–80% of the rated capacity as usable, depending on the system. So a 500 Wh unit might reasonably support about 300–400 Wh per charge under real conditions. Using that idea, the sample 470 Wh plan is probably too optimistic. You could adjust by:

Running the fan fewer hours
Using only one lamp instead of two
Charging the laptop less or using it in low-power mode

These trade-offs are easier when you understand what each watt and watt-hour means for your daily habits.

Matching Backup Power to Different Living Situations

Not every home needs the same level of backup. A small apartment, a single-family house, and a home with frequent winter storms may all benefit from different approaches. Understanding watts vs watt-hours lets you tailor your plan instead of buying more than you need or, just as frustrating, not enough.

Renters and Small Apartments

If you rent or live in a small space, you may have limited storage and fewer options for installing large systems. In this case, it can help to focus on low-watt essentials and smaller, portable battery-based setups.

Helpful strategies include:

Favoring LED lighting and low-watt fans
Choosing devices that can charge via USB where possible
Using a single small power station for phones, router, and a lamp
Keeping high-watt appliances, like space heaters, off your backup plan

Because you are likely dealing with modest watt-hour capacity, being selective about what you run makes each watt-hour count more.

Single-Family Homes and Larger Loads

In a house, you may want to keep more things going: a refrigerator, garage door opener, or sump pump. These can require higher watts and significant watt-hours over time.

For these larger loads, consider:

Listing high-priority circuits or devices (such as fridge and a few outlets)
Checking their watt requirements, including motor surge watts
Planning for partial use instead of continuous use (for example, running a refrigerator periodically rather than all day on backup)
Separating comfort loads (TV, gaming systems) from essential loads

Because these systems can draw more watts, it is important to confirm that any inverter or backup system you use is properly sized and safely installed, especially if connected to home wiring.

Families with Kids, Seniors, or Pets

Households with different age groups and pets often care more about comfort and routine. A bit of power used in the right way can make blackouts less stressful for everyone.

Some realistic uses of low to moderate watts include:

Night lights or dim lamps for children who wake up at night
Charging devices used for reading or listening to stories
Keeping pet fans, water fountains, or small filters running for limited hours
Charging mobility aids or communication devices for older adults

In these cases, understanding watt-hours helps you see how much “room” you have for comfort items after covering true essentials.

Using Solar to Refill Your Watt-Hours

For outages that last more than a day, some people add small solar panels to help refill their battery or power station. Solar adds another variable, but the same watt and watt-hour principles apply.

What Solar Panel Watts Really Mean

Solar panels are usually rated by watts under ideal test conditions. For example, a panel might be labeled 100 W. In real life, several factors reduce its output:

Season and sun angle
Clouds and haze
Panel temperature
Shading from trees or buildings

As a rough planning idea, many people assume they might get around 3–5 hours per day of near-rated output in good conditions, depending on location and season. That means a 100 W panel might produce on the order of a few hundred watt-hours in a day in favorable weather, but less in winter or during storms.

Balancing Daily Use and Daily Recharging

To use solar effectively:

Estimate your daily watt-hour use from your priority devices.
Estimate your best-case daily solar watt-hours from your panel setup.
Aim to keep use at or below what you can reasonably replace over a day or two.

For instance, if your small setup might realistically collect about 300 Wh per day in good sun, planning for 200 Wh of daily use gives you margin for clouds and inefficiencies. With this mindset, you are not guessing; you are managing a daily watt-hour budget.

Table 2. Example device watt ranges and blackout planning notes. Example values for illustration.

Device type	Typical watts range (example)	How to think about runtime	Planning note
Smartphone charger	5–20 W	Short charging bursts; low daily Wh	Easy to cover on small battery packs
Wi‑Fi modem/router	10–20 W	Often left on for hours; moderate daily Wh	Decide how many hours you truly need it
LED lamp	5–10 W	Can run many hours on modest Wh	Use these instead of higher-watt bulbs
Laptop	30–60 W	Uses more Wh over long work sessions	Limit use or lower brightness to save Wh
Small fan	30–70 W	Comfort vs. battery drain trade-off	Run in shorter blocks, not all day
Refrigerator (average)	80–150 W	Runs in cycles; needs more daily Wh overall	Plan for startup surges and limit door openings
CPAP or similar medical device	30–80 W	Often needs overnight hours; important Wh load	Check exact device specs and plan with margin

Simple Ways to Stretch Your Backup Power

Once you understand watts and watt-hours, you can take small steps to make your existing backup power go further without adding more equipment.

Lower the Watts You Need

Choose lower-watt alternatives where possible, such as LED bulbs instead of older incandescent bulbs.
Run one shared lamp or room light instead of multiple lights around the home.
Use battery-powered lanterns or flashlights for walking around, saving your main backup power for plug-in devices.
Use fans for personal cooling instead of trying to run high-watt air conditioners.

Shorten the Time Devices Run

Charge phones and laptops fully, then unplug them to save inverter overhead.
Turn off the router when not actually using the internet.
For refrigerators, keep the door closed to reduce how often the compressor runs.
Set specific “power-on windows” each day instead of leaving everything on continuously.

Organize a Simple Power Plan for Your Household

Before the next storm season or heatwave, consider writing a short, clear backup power plan for your home:

List which outlets, power strips, or circuits connect to your backup source.
Note which devices are “OK to use” and which should stay off during outages.
Set target watt-hour budgets for day and night, even if they are rough estimates.
Talk through the basics with other household members so they know how to help conserve power.

A bit of planning with watts and watt-hours in mind turns backup power from a mystery box into a tool you can use confidently, whether you live in a studio apartment or a larger family home.

Frequently asked questions

What is the practical difference between watts and watt-hours?

Watts measure how much power a device uses or a source provides at an instant, while watt-hours measure the total energy used or stored over time. Use watts to check whether a backup can run a device at all, and watt-hours to estimate how long it will run.

How do I estimate how long a battery will run my devices?

Add the watts of all devices you plan to run at the same time to get the total continuous load, then divide the battery’s watt-hours by that total to get an ideal runtime. Allow for inverter losses and battery depth-of-discharge by reducing usable Wh (a common planning range is about 60–80% of rated Wh) and ensure the total load is below the backup’s continuous watt rating.

Why do refrigerators need higher surge watts and how should I plan for that?

Refrigerators have compressors that require a short startup surge of current several times higher than their running watts. When sizing backup power, check both the running and surge watt ratings of the appliance and choose an inverter or generator with sufficient surge capacity and some additional margin for repeated starts.

How can I convert amp-hours (Ah) to watt-hours (Wh) for a battery?

Estimate watt-hours by multiplying the battery voltage by amp-hours: Wh ≈ V × Ah. Then account for usable capacity — many battery chemistries shouldn’t be fully drained, so plan using a reduced Wh figure based on recommended depth-of-discharge.

How many solar panel watts do I need to recharge a battery during an outage?

Estimate your daily Wh need, then divide by the expected peak sun hours per day (commonly 3–5) to get required panel watts, and add margin for charging and inverter losses and cloudy days. For example, 600 Wh per day divided by 4 peak sun hours implies about 150 W of panels before accounting for real-world losses, so choose more capacity to be safe.

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