Why a browser can't test your LAN's maximum speed

You may want to know whether your home network can transfer files at its full speed, but a browser speed test reports a different thing. It measures the connection between your device and a test server on the internet, not the maximum throughput between devices on your local network.

The Speed Test can help you check download speed, upload speed, ping and jitter on your internet connection. To measure the LAN itself, you need a test that sends data between two devices on that LAN.

Check what the browser speed test measures

1. Open the Speed Test on the device and network you want to check.
2. Pause downloads, video streams and cloud backups on the network, if you can. Other traffic can use some of the available capacity.
3. Run the test and note the download, upload, ping and jitter results. These show how the connection to the test server performed at that moment.
4. For a useful comparison, repeat the test under similar conditions on another device or with the computer connected by Ethernet. Keep in mind that both tests still measure the internet route, not the LAN's maximum.

What the result means

The result is close to your internet plan's speed

Your device can transfer data to and from the test server at roughly that rate under the conditions of the test. This does not tell you the LAN's top speed. Your router, Ethernet ports or Wi-Fi may support a faster local transfer than your internet plan provides.

The result is much lower than expected

Something along the route to the server may be limiting the result. Possible causes include a slow Wi-Fi connection, another device using the internet, a VPN, the router, your internet provider or the test server's route. A low result alone does not show that your LAN is slow.

Two devices get similar results

Both devices may be reaching a similar limit on the internet connection, even if one is connected by Ethernet and the other by Wi-Fi. That comparison can help identify a Wi-Fi problem, but it still cannot reveal the full speed available between the devices on your LAN.

A file copies more slowly than the speed test suggests

The speed test and file copy use different routes and conditions. A file copy can be limited by the sender's drive, the receiver's drive, file-sharing software, Wi-Fi, or the speed of a network adapter. Internet download speed is not a promise that a local file will copy at the same rate.

How to measure your LAN instead

1. Choose two devices on the same network. Both must connect through the same router or network switch. Use devices with wired network ports if you want to check a wired link.
2. Run a local throughput test between them. A tool such as iperf3 sends data from one device to the other and reports the transfer rate. It needs to be installed on both devices, with one set up as the test server and the other as the client. Follow the tool's instructions for your operating systems and allow the connection through any firewall prompt.
3. Compare wired and Wi-Fi results separately. Test the same two devices over Ethernet, then over Wi-Fi if you want to see how much the wireless link changes the result. Keep the devices in the same locations for each comparison.
4. Check a real file transfer if that is what matters to you. Copy a large file between a computer and a network drive. This shows practical transfer performance, but it also includes the speed of both storage devices and the file-sharing method, so it is not a pure measure of network capacity.

For a wired link, the negotiated link rate is a useful clue, but it is not the same as measured throughput. For example, a 1 Gbps link has a theoretical maximum of 125 MB per second before network overhead, and real file transfers are usually lower.

Why a browser test has limits

A browser page runs inside a security sandbox. It cannot freely send arbitrary network packets, open a listening port on your computer, or automatically find and test every device on your private network. Those restrictions help prevent websites from probing devices and services without your knowledge.

A browser could transfer data to a web server that you deliberately run on your LAN. The result would still measure the whole path between the browser and that server, including the browser, operating system, network adapters and server. It would not simply reveal the maximum capacity of your router or Wi-Fi radio.

Browser tests also use normal web connections and depend on the browser and device keeping up with the transfer. At high rates, processor load, memory use, protocol overhead and the test server can affect the result. That makes a browser speed test useful for checking internet performance, but not a universal LAN capacity meter.

Keep internet and local tests separate

Use the browser test to check the internet connection from your device. Use a local transfer test to compare devices on your LAN. The TooLab Speed Test exchanges test data with our server to measure your internet connection, so its result is about that route, not private device-to-device traffic.