How Many Watts Does a Modem Use?

Last updated: August 26, 2026

Modems are among the lowest-power devices in a home, but they normally run 24 hours a day. That makes their wattage relevant for three reasons: electricity use adds up over time, even a small battery can keep a modem running for hours during an outage, and the difference between powering only a modem and powering your entire internet connection can dramatically change backup runtime.

The last point is the one that causes the most confusion. Keeping a cable modem powered does not necessarily give you usable Wi-Fi. Many homes also need a separate router. Fiber customers may need an optical network terminal, or ONT. Mesh systems and Ethernet switches can add still more continuous load.

How Many Watts Does a Modem Use?

For a typical U.S. home internet setup, a useful starting point is:

These are planning ranges rather than universal specifications. Your own equipment may fall outside them.

Modem vs. Router vs. Gateway vs. ONT: Know What You Are Measuring

Before calculating wattage, identify which boxes actually have to stay powered. The word “modem” is often used loosely for several different devices.

Modem

A cable or DSL modem connects your home network to your internet service provider. A standalone modem normally does not provide the Wi-Fi coverage your phones and laptops use.

Wi-Fi Router

A router creates your local home network and usually broadcasts Wi-Fi. If your modem and router are two separate boxes, both generally need power for normal wireless internet access.

Gateway

A gateway combines the modem and router into one unit. ISP-provided equipment from companies such as Xfinity and Cox is commonly designed this way. Because a gateway also runs Wi-Fi radios and routing hardware, it can use noticeably more power than a basic standalone modem.

Fiber ONT

Fiber internet usually uses an optical network terminal instead of a traditional cable modem. If the ONT loses power, your router can remain powered and continue broadcasting a Wi-Fi network, but that Wi-Fi may have no internet connection.

Mesh Nodes and Network Switches

Mesh Wi-Fi nodes, Ethernet switches, PoE equipment and other networking hardware add their own continuous load. During an extended outage, turning off nonessential nodes can meaningfully increase battery runtime.

For a complete outage setup, see UDPOWER's guide to keeping Wi-Fi and internet running during a power outage.

Real-World Modem Power Consumption Examples

Actual published measurements show why one universal modem wattage number does not work. Basic cable modems can remain in the single digits, while advanced gateways with several network interfaces and Wi-Fi radios may exceed 20 watts.

The takeaway is more useful than memorizing any individual model: basic standalone modems tend to be very small electrical loads, while all-in-one gateways can consume two or three times as much power.

How Much Electricity Does a Modem Use per Day?

Watts describe the rate at which the modem is using power. Your electric bill is based on energy consumed over time, normally measured in kilowatt-hours.

Because modems generally stay powered around the clock, even a small difference in wattage appears in annual energy use.

How Much Does It Cost to Run a Modem?

Multiply monthly kWh by the electricity rate on your utility bill.

For example, at a hypothetical electricity price of $0.20 per kWh:

• A 10W modem uses about 7.2 kWh per month, costing roughly $1.44.
• A 20W gateway uses about 14.4 kWh per month, costing roughly $2.88.
• A 30W complete network setup uses about 21.6 kWh per month, costing roughly $4.32.

Use the rate from your own electric bill rather than relying on a national average, since residential rates vary significantly by state and utility.

How to Find Your Modem's Actual Wattage

If you need an accurate number for battery backup or electricity calculations, use the following methods in order of accuracy.

That does not mean the modem continuously consumes 12 watts. It means the adapter is capable of supplying up to approximately 12 watts on its DC output under its rated conditions.

What Affects Modem Power Consumption?

DOCSIS Generation and Hardware

Newer cable modems may contain faster processors, more channels and higher-speed Ethernet interfaces. That does not automatically mean every newer modem draws more power, but performance features can increase the electrical load.

Integrated Wi-Fi

A standalone modem only handles the internet connection. A gateway may also run multiple Wi-Fi radios, antennas, routing, firewall functions and smart-home connectivity. This is why gateway wattage can be much higher.

Ethernet Speed

Multi-gigabit Ethernet interfaces require more capable networking hardware than basic Gigabit Ethernet. The effect varies by design, but it is another reason not to assume every DOCSIS 3.1 modem consumes the same power.

Voice and Additional Network Functions

ISP gateways may include telephone service, Bluetooth, Zigbee, MoCA or additional networking hardware. CableLabs equipment listings demonstrate how dramatically the feature set can differ between models.

Operating State

Power consumption can change during startup, firmware activity or network operation. For backup sizing, a normal steady-state measurement is usually more useful than the largest instantaneous number you observe.

For an Outage, Do Not Calculate the Modem Alone

This is the most important practical lesson in this guide.

If your goal is simply to answer “how many watts does my modem use?”, measure the modem. If your goal is to keep the internet working during a blackout, measure everything that has to remain on.

UDPOWER's broader portable power station outage runtime guide uses a similar approach: add every essential device first, then size the battery from the complete continuous load.

How Long Can a Portable Power Station Run a Modem?

Modems and routers are unusually good candidates for battery backup because their continuous power demand is small.

For UDPOWER runtime planning, the following estimates use approximately 90% conversion efficiency:

Using current UDPOWER battery capacities, the theoretical planning estimates are:

These are planning estimates, not guaranteed runtimes. Actual results depend on the power station's own operating consumption, AC inverter efficiency, temperature, battery condition, attached equipment and power-saving behavior.

You can also enter your measured load and battery capacity into the UDPOWER Portable Power Station Runtime Calculator.

Which UDPOWER Power Station Makes Sense for a Modem and Router?

You do not need hundreds or thousands of watts of output just to run network equipment. For internet backup, battery capacity and low-load runtime matter far more than maximum AC output.

That means the best choice depends primarily on how long you want the network to stay online and whether you also plan to power phones, laptops, lights or other emergency equipment.

Best for Short Internet Outages

UDPOWER C400 Portable Power Station

The UDPOWER C400 has a 256Wh LiFePO4 battery and 400W rated AC output. A modem and router only use a small fraction of that output capacity, making the C400 better suited to this job than its watt rating might suggest.

Using a 20W network load and a 90% planning efficiency, 256Wh provides approximately 11.5 hours of calculated runtime before accounting for additional low-load inverter overhead.

• 256Wh battery capacity
• 400W rated AC output
• LiFePO4 battery chemistry
• 4,000+ cycle positioning on the current product page
• Two AC outlets for a separate modem and router
• Supports multiple charging methods including solar

View UDPOWER C400

Best for Overnight or Full-Day Internet Backup

UDPOWER C600 Portable Power Station

For longer outages, the UDPOWER C600 increases battery capacity to 596Wh while providing 600W rated output.

At a continuous 20W modem-and-router load, the same 90% planning formula gives approximately 26.8 hours. A 30W network setup calculates to approximately 17.9 hours.

• 596Wh LiFePO4 battery
• 600W rated output
• 4,000+ cycle positioning
• Multiple AC, USB and DC outputs
• Up to 240W solar input listed on the current product page
• 5-year warranty protection for UDPOWER power stations

View UDPOWER C600

If your backup plan also includes laptops, lighting, refrigeration or other emergency loads, compare the full UDPOWER portable power station lineup rather than sizing the battery from the modem alone.

How to Make Your Internet Backup Last Longer

1. Power Only the Network Equipment You Actually Need

During a long blackout, there is little benefit in keeping three mesh nodes running if the main router covers the part of the house you are using. Every always-on device reduces runtime.

2. Separate Network Backup From High-Draw Appliances

A modem and router may use only 20–30W. A microwave, electric kettle, heater or hair dryer can consume hundreds or more than a thousand watts. A few minutes of high-power appliance use can consume energy that would otherwise keep your network online for many hours.

3. Keep Using the Original AC Adapters Unless You Know the DC Requirements

Some network equipment runs internally on DC power, and direct DC operation can sometimes avoid AC conversion losses. However, voltage, connector size and polarity must match exactly. For most users, the safest and simplest option is the manufacturer's original adapter plugged into the power station's AC outlet.

4. Measure the Whole Network With One Watt Meter

This gives you a better runtime estimate than adding maximum adapter ratings together.

5. Create a Dedicated Outage Configuration

If you have a large home network, decide in advance which router, mesh node and switch are truly required. An “outage mode” can reduce a 40–50W network to 20–30W and significantly increase runtime.

6. Save Phones and Laptops for Intermittent Charging

Do not leave every device connected to the backup battery continuously. Charge mobile electronics when needed rather than turning a low-power internet backup into a general charging station.

Remote workers can also use the load-planning approach in UDPOWER's remote work setup and backup power guide.

Can the Modem Have Power but the Internet Still Be Down?

Yes.

A battery can keep equipment inside your home running, but it cannot guarantee that your internet provider's infrastructure remains operational.

During a widespread outage, several things can happen:

• Your router continues broadcasting Wi-Fi but the modem or ONT has no connection.
• Your own modem and router work normally, but neighborhood cable equipment has lost power.
• Your ISP's backup batteries eventually run out during a prolonged outage.
• A physical cable or fiber line is damaged by the same storm that caused the electrical outage.
• The provider experiences a network outage unrelated to your home power.

For emergency planning, keep a cellular hotspot or phone tethering option available when possible. During major storms and regional outages, having two independent communication paths is more useful than simply buying a larger battery.

So, What Wattage Should You Actually Use?

If you came here because you need one number, use the following:

• 10W as a quick planning figure for a basic standalone modem.
• 20–25W for many all-in-one modem/router gateways.
• 20–30W for a basic separate modem + Wi-Fi router setup.
• 30–40W+ when mesh nodes, switches or other networking equipment must stay powered.

Those figures are good for preliminary planning. For a battery purchase or a multi-day outage strategy, measure your exact setup.

Frequently Asked Questions