Fiber optic is the fastest access technology available, but the speed on your contract is not always what you actually receive. A fiber speed test measures the real traffic between your home and a remote server, both download and upload.
How does a fiber speed test work?
The test sends and receives data between your browser and a measurement server. It reports three main metrics: download speed, upload speed and latency (ping). Jitter completes the picture by measuring ping variation, which matters for video calls and online gaming.
Test duration and server distance affect the result. For a reliable measurement, choose a server close to your location and run the test two or three times.
What is a normal fiber speed?
Real speed depends on your plan, your equipment and how you connect. Here are typical ranges observed in France:
| Fiber plan | Typical download | Typical upload | Note |
|---|---|---|---|
| 300 to 500 Mbps | 250 to 480 Mbps | 200 to 450 Mbps | Often limited by Wi-Fi |
| 1 Gbps | 850 to 950 Mbps | 600 to 900 Mbps | 1 Gbps Ethernet port required |
| 2 Gbps | 1.5 to 1.9 Gbps | 1 to 1.8 Gbps | 2.5 Gbps network card recommended |
| 5 to 8 Gbps | 3 to 7 Gbps | 2 to 7 Gbps | 10 Gbps hardware required |
A result 10–20% below the advertised speed is common. A gap of 50% or more is worth investigating.
Why is your fiber speed lower than expected?
Wi-Fi
This is the most common cause. Wi-Fi loses speed with distance, walls and interference. A Wi-Fi test does not measure fiber itself, but the quality of your wireless network.
Network hardware
A 100 Mbps network card, a damaged Ethernet cable or an old router can cap your speed. Check that your card, cable and router support at least 1 Gbps.
The test server and time of day
A busy server or peak-hour congestion can distort the result. Test at different times of day and with different servers.
Your home and installation
A poorly connected fiber socket, a faulty ONT box or a building served by another technology (FTTB, cable) can reduce speed. In that case, contact your ISP.
How to test your fiber speed properly
- Connect a computer directly to the router with an Ethernet cable.
- Close downloads, updates and VPNs.
- Restart the router and wait for it to sync.
- Choose a server close to your location.
- Run three tests and keep the average.
- Run a Wi-Fi test afterwards for comparison.
Key point: a wired test close to the advertised speed confirms that fiber is working. If Wi-Fi is slower, the wireless network is the problem, not the line.
FTTH, FTTB and cable: what is the difference?
FTTH (Fiber to the Home) brings fiber all the way to your home. FTTB (Fiber to the Building) stops at the building and then uses cable or copper. Coaxial cable shares bandwidth between neighbours, so speeds and stability can vary.
What if your fiber speed stays low?
Start by testing again over Ethernet with a recent cable. If the speed remains far below your plan, note your results, the time of the test and the server used, then contact your ISP. These details help them identify a line or equipment problem.
Frequently asked questions
Why does my fiber test show 500 Mbps when I pay for 1 Gbps?
Wi-Fi, a 1 Gbps network card, a Cat5e cable or a distant server can limit the measurement. Test over Ethernet with a recent cable and a nearby server.
Should I test my fiber over Wi-Fi or Ethernet?
Use Ethernet to measure the line and Wi-Fi to measure the real experience on your devices. The two tests are complementary.
Does a speed test use a lot of data?
Yes, a full test can use several hundred megabytes, or even several gigabytes depending on duration and speed. Avoid running it on a limited 4G/5G plan.
What should I do if the speed stays low after several tests?
Check the cable and network card, restart the router and test again. If the wired speed remains far below your plan, contact your ISP with your results.
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