GPS Speedometer
Open this page on your phone and press Start to see how fast you are moving, measured by GPS. It records your maximum and average speed and the trip distance, warns you above a speed limit you choose, and has a mirrored HUD view for reflecting onto a windshield at night.
Last updated:
Over the speed limit
Press Start to read your speed from GPS. Works best on a phone, outdoors, with a clear view of the sky.
For safety, set everything up before you drive and let a passenger handle the phone. GPS speed can lag by a second or two and is not a legal reference.
How to use the GPS Speedometer
- Open the page on your phone and choose mph, km/h, knots or m/s.
- Press Start speedometer and allow location access. Wait outdoors until the GPS dot turns green.
- Set a speed limit if you want an alert, using the box or a preset sign.
- Open HUD mode for a large mirrored display, and lay the phone flat on the dashboard at night.
- Check your trip: max speed, moving average and distance update as you go; press Reset trip to start over.
How GPS measures speed
Your phone can work out speed in two ways. The better one uses the Doppler shift of the satellite signals: as you move toward or away from each satellite, the frequency the receiver hears changes slightly, and from those changes the chip calculates your velocity directly. Most phones report this as the location's speed value, and this page uses it whenever it is available.
If the device does not report speed, the page calculates it from consecutive positions: speed = distance between two fixes ÷ time between them, with distance from the haversine formula on a sphere of radius 6,371 km. Because each fix has an error of a few meters, the calculated speed is smoothed and tiny movements smaller than the fixes' accuracy are ignored.
Average (moving) is the trip distance divided by the time you were moving faster than 0.5 m/s, so stops at traffic lights do not drag it down. Trip time counts all the time the speedometer was running.
Speed unit conversions
| Unit | Equals in m/s | 1 m/s equals | Used for |
|---|---|---|---|
| Miles per hour (mph) | 0.44704 | 2.23694 mph | Roads in the US and UK |
| Kilometers per hour (km/h) | 0.27778 | 3.6 km/h | Roads in most other countries |
| Knots (kn) | 0.51444 | 1.94384 kn | Boats, sailing and aviation (1 kn = 1 nautical mile per hour = 1.852 km/h) |
| Meters per second (m/s) | 1 | 1 m/s | Science, wind speed, running |
Quick checks: 60 mph = 96.6 km/h = 52.1 knots = 26.8 m/s; 100 km/h = 62.1 mph = 54.0 knots.
Getting the most reliable readings
- Give it a clear sky. Wait until the indicator shows GPS good (accuracy of 25 m or better) before relying on the numbers. Windshields with metallic coatings can weaken the signal; a spot near the edge of the glass often works better.
- Keep the page in front. Mobile browsers pause location updates when the screen locks or you switch apps. The page asks the phone to keep the screen on while tracking, but plug the phone in on long trips.
- Expect gaps in tunnels and cities. Tall buildings reflect signals and can cause short spikes. Max speed only counts fixes with an accuracy of 50 m or better to filter most of them out.
- Use it for cycling, running, boating or as a backup when a vehicle speedometer is broken. For running pace, the pace to speed converter turns min/mile into mph.
Frequently asked questions
How accurate is a GPS speedometer?
With a good satellite fix, phone GPS speed is usually within about 1 to 2 km/h (around 1 mph) at steady speeds, because it is measured from the Doppler shift of satellite signals rather than from position jumps. It can lag a second or two when you speed up or brake, and it is less reliable in tunnels, between tall buildings and indoors.
Why does my GPS speed differ from my car's speedometer?
Car speedometers are allowed to read high, never low, so most show 2 to 10 percent more than your true speed. GPS measures your actual speed over the ground, so a slightly lower GPS reading is normal.
Why does it show 0 or jump around when I'm standing still?
Every GPS fix has some position error, which can look like movement. The speedometer treats anything below 0.5 m/s (about 1 mph) as stationary and ignores small position wobbles when adding up distance, so drift does not inflate your trip.
How does HUD mode work?
HUD mode shows huge mirrored digits on a black screen. Lay the phone flat on the dashboard, screen up, so its reflection appears in the windshield; with Mirror on, the reflected numbers read the right way round. If they appear upside down, turn the phone around or switch Flip on. It works best at night.
Does it work on a laptop?
Most laptops have no GPS and estimate location from Wi-Fi, which is only accurate to tens of meters and updates rarely, so speed readings will not be useful. Use a phone or tablet with GPS.
Does it use mobile data or send my location anywhere?
GPS itself works without data, and once the page is loaded the speedometer keeps working. Your position is only processed in your browser and is never uploaded or stored.
Is it safe to use while driving?
Set up the units, limit and HUD before you start, mount the phone securely or let a passenger hold it, and never interact with it while driving. Always follow posted speed limits and your vehicle's speedometer.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.