How It Works
A short, jargon-free explanation of GPS-based speed measurement and what to expect when using Train Speed Test on a moving train.
GPS in 30 Seconds
Your phone or laptop has a tiny GPS receiver that listens to signals from satellites orbiting Earth. By measuring how long these signals take to arrive, it can pinpoint your location within a few meters. When you're moving, it samples your position multiple times per second and calculates your speed by dividing distance by time. Train Speed Test simply reads that speed value through your browser's Geolocation API and displays it.
Allow Location Access
On first use, your browser will pop up asking for permission to share your location. Click Allow. Train Speed Test never sees your raw coordinates — it only reads back your derived speed.
Find a Window Seat
GPS needs a line-of-sight to satellites. The closer you are to a window, the more satellites your device can see and the more accurate your readings will be.
Wait for First Fix
It can take 10–30 seconds for your device to lock onto enough satellites. Once it does, the dial starts updating about once per second.
Keep the Screen On
Most browsers pause GPS when your screen turns off. If you want continuous tracking, keep the tab visible and consider plugging into power for long trips.
Privacy
Everything happens in your browser. Your GPS coordinates are never sent to a server, stored in a database, or shared with any third party. Close the tab and the data is gone.
For more detail, read our Privacy Policy.
When Readings Go Wrong
- Speed drops to 0 — usually a tunnel, underground station, or steel-shielded coach. Resumes when GPS regains signal.
- Jittery numbers — the train is stopped or going very slowly. GPS noise becomes more noticeable below ~10 km/h.
- Inconsistent max speed — short bursts of GPS error can spike the maximum. Use the Reset button to clear stats.
- Speed unavailable — some browsers don't report speed directly. Train Speed Test falls back to calculating speed from consecutive coordinates using the haversine formula.
Try Our Tools
Explore more travel and measurement tools to make your journey easier and more informative.
Train Speed Test
Measure the real-time speed of the train you're traveling in using your device's GPS, with smooth analog and digital readouts.
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Convert between km/h, mph, m/s, and knots instantly. Useful for understanding speed readings from different sources.
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