How to Fix Ethernet Speed Capped at 100 Mbps on Windows

A durable and reliable Ethernet connection is required to enjoy the full potential of a high-speed fiber broadband, especially for desktop users. But users often find their Ethernet speed capped at 100 Mbps, even on a Gigabit Ethernet. This guide attempts to resolve this strange but common error affecting many Windows users.

Tip: is your Ethernet connection not working? Try these fixes.

When you connect Ethernet cables to your computer or router, you should notice an audible click or snap once the cable is firmly in place. Sometimes the Ethernet cable is not fully connected, or the "clip/tab" on the cable connector (RJ45 connector) becomes loose or breaks entirely. This can cause the connection between the connector and the computer/router to become less stable.

A loosely-connected cable can cause a speed drop for a high-speed 200 Mbps/300 Mbps or faster connection where the network will default to 100 Mbps.

To fix this, disconnect the Ethernet cable from both your router and computer and reconnect it after around 30 seconds. Ensure that the cable is tightly connected at both ends. Even with a broken clip, you can push the cable all the way into the LAN port to eliminate a loose connection as the source of the capped speed.

If all of your Ethernet connections are in good order, the issue might lie with the cable itself. Ethernet cables are classified according to their data transfer capabilities. Common Ethernet cables used in home and office networks are Cat5, Cat5e, and Cat6. Less commonly used cables are Cat6a, Cat7, and Cat8.

If your home network is using a Cat5 Ethernet cable, your speeds will be limited to a maximum of 100 Mbps, as that's the data transfer limit of Cat5 cables. Hence, you may just need to replace your cable with a cable that's at least Cat5e, which is capable of transferring data up to 1000 Mbps.

To identify the type of Ethernet cable you currently have, look at the sheath of the cable. You will be able to find text written on the sheath that will mention whether the cable is Cat5, Cat5e, Cat6, or something else. If you don't find any text on the cable sheath, it'll be difficult to identify the cable type, as there are only minor differences in thickness and internal wiring between the different types of cables. For more details, check out the things to know when buying Ethernet cables.

Switching from a lower bandwidth cable like Cat5 to a higher one like Cat5e or Cat6 should ideally fix the issue of capped Ethernet speeds. But if you're still experiencing intermittent speed drops on your Gigabit connection, it's possible that the RJ45 connectors at the ends of the Ethernet cable are the culprits.

Often, home setups involve routing the Ethernet cable internally within the walls. This is both for achieving a cleaner look as well as protecting the cable from damage. The default RJ45 connectors that are pre-applied to the cable ends are often too big and need to be removed before routing the cable through the walls. This inevitably requires "re-crimping" or reconnecting new connectors to the cable ends once they come out at the other end.

It is at this stage that issues will creep up. Either the new RJ45 connector used is incompatible with the cable's internal wires, or the re-crimping process is wrong. If even one of the internal wires is not connected properly to the connector's metal contacts, your connection speed will drop to 100 Mbps.

Hence, consider replacing your RJ45 connectors with shielded, high-quality ones. It's advisable to do this only after you've already replaced the cable itself and the issue still persists.

Good to know: these methods may help you fix a slow Wi-Fi connection in your home.

If you've eliminated the physical sources behind the error, it's time to move on to the software side of things. Your computer's Ethernet adapter settings could potentially be limiting your connection speed to 100 Mbps. There are multiple settings here that need to be checked. To ensure your adapter settings are correctly configured, follow the steps below:

Configuring the settings in the previous section properly should solve the low-speed issue for most users. But if you're still unable to fix it, you can try updating your Ethernet adapter drivers. Outdated drivers can often cause a variety of issues, one of which can be capped Ethernet speed.

Tip: unlock more settings by installing custom firmware on your router.

Some routers have settings configured in a way that reverts your connection to a "lite or green" mode, where the network speed is capped at 100 Mbps. This can be one of the reasons for the low-speed issue for many users. You can log in to your router's settings and reconfigure the settings to solve the issue by following the steps below:

Good to know: learn the difference between the "Access Point" and "Repeater" modes on your router.

A Cat5e Ethernet cable is technically capable of Gigabit speeds, but is inferior to Cat6 cables in terms of grounding and overall cable durability. This is a common source of failure in Cat5e cables that can lead to unstable connections and dropped speeds, even though they are technically certified for up to 1 Gbps speeds. It's better to go for a higher-grade Cat6 cable to minimize the chances of cable-induced connection issues.

The 2.4 GHz band can technically support speeds of up to 1.2 Gbps on Wi-Fi 6 routers when paired with a fast enough Internet plan. But in practical situations, most people using the 2.4 GHz band likely have Wi-Fi 4 or 802.11n routers, as Wi-Fi 5 only supports the faster 5 GHz band. In these situations, the 2.4 GHz band's theoretical maximum is around 300 Mbps. But with other factors like interference from other devices and the crowding from other networks on the 2.4 GHz band, actual speeds get decreased even further. In general, you can expect less than half of your plan's rated speed on the 2.4 Ghz band. Try band steering to get the most out of your 2.4 GHz and 5 GHz bands.

Yes, Ethernet cables have a rated distance limit beyond which the transfer speeds tend to fall off significantly. For instance, Cat7 cables can transfer up to 100 Gbps, as long as the cable length is within 15 meters or 50 feet. Distance limits for Cat6 or Cat5 are more relaxed and can retain most of their speed until around 100 meters or 300 feet. In practice, you'll rarely find cable lengths reaching 300 feet in home setups. Therefore, speed reduction due to distance isn't as much of an issue.

To support Internet speeds of more than 100 Mbps, you need a Gigabit router. Your ISP or Internet Service Provider typically provides a compatible Gigabit router for modern high-speed fiber broadband plans. But if you have an older model you already own and are routing your Internet through that, you may want to check whether your router supports Gigabit. You can check the model of your router printed on its front or back, then check its specifications online.

Image credit: Unsplash. All screenshots by Tanveer Singh.

Tanveer hunts far and wide for PC Hardware, Windows, and Gaming ideas to write about. An MBA in Marketing and the owner of a PC building business, he has written extensively on Technology, Gaming, and Marketing. When not scouring the web, he can be found binging on The Office, running for his life in GTFO, or wrecking karts in Smash Karts.

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