Local Network
LAN Speed Test: Test Speed Between Local Devices
The LAN Speed Test measures throughput between devices on your local network without crossing your internet connection. It verifies that your gigabit Ethernet, NAS, and managed switches are actually delivering the speeds they advertise rather than being capped by a bad cable or misnegotiated link.
What It Measures
This tool measures local area network throughput in megabits per second between two devices on the same LAN. It also detects link speed, duplex mode, and any retransmissions that suggest cable or switch problems.
How It Works
- Establishes a TCP connection to a target device on your local network
- Pushes large data transfers in both directions
- Measures sustained throughput and TCP retransmission count
- Compares result to expected link speed (1 Gbps, 2.5 Gbps, 10 Gbps) and reports efficiency
Why It Matters
Gigabit Ethernet should deliver around 940 Mbps of usable throughput. If your NAS to laptop transfer crawls at 100 Mbps, your link probably negotiated to 100BASE-TX instead of 1000BASE-T due to a damaged cable, an old switch port, or a duplex mismatch. LAN testing isolates these problems from any internet related issues.
Understanding Your Results
Gigabit Ethernet should sustain 900 Mbps or more. 2.5 Gbps links should deliver 2.3 Gbps or more. 10 Gigabit Ethernet should reach 9 Gbps in optimal conditions. Anything below 50% of the link rate indicates cable, switch, or NIC issues. Zero retransmissions is ideal; even a small percentage suggests cable damage.
Frequently Asked Questions
Why is my gigabit network slow?
Common causes include damaged or old Cat 5 cables (only Cat 5e or better supports gigabit), a switch port that has negotiated to 100 Mbps, an outdated Ethernet adapter driver, or a CPU bottleneck on the source or destination device. The LAN test will confirm whether the link itself is the issue.
How do I test LAN speed without another device?
If you only have one device, you cannot run a true LAN test (you need two endpoints). Workarounds include using your phone as the second device with a USB Ethernet adapter, or running the test against your router (some routers support this). Otherwise, use the Local Network Speed tool which measures your loopback throughput.
What cable do I need for gigabit Ethernet?
Cat 5e is the minimum for gigabit. Cat 6 supports 10 Gbps over short runs (up to 55 meters). Cat 6a supports 10 Gbps over the full 100 meter Ethernet limit. If your cables are old or unmarked, they may be Cat 5 (not 5e) which limits to 100 Mbps. Replacing cables is cheap and often resolves slow LAN issues.
Can WiFi achieve gigabit speeds?
WiFi 5 (802.11ac) can theoretically deliver 1.3 Gbps but real world speeds are usually 200 to 600 Mbps. WiFi 6 (802.11ax) and WiFi 6E push real world speeds to 1 Gbps or higher under good conditions. WiFi 7 can exceed wired gigabit speeds. For consistent gigabit performance, wired Ethernet remains the best choice.
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