Is GPS speed more accurate than my car's speedometer?

Yes. Car speedometers are legally required to never show less than the actual speed, so they typically read 2-5% higher than actual speed. GPS measures your true ground speed.

Does this work while driving?

Yes, but mount your phone safely and don't interact with it while driving. Have a passenger operate it for safety.

Why does my GPS speed differ from my dashboard?

Car speedometers are calibrated to read slightly high for legal reasons. Tire size changes also affect dashboard accuracy. GPS measures actual ground speed.

Car Speed Test (GPS Browser Tool)

Measure your real vehicle speed directly through your browser using GPS sensors. No installs. No signup. Works on iOS & Android.

❌ GPS Disconnected

Quick Instructions

1️⃣
Allow location permissions
Grant access when your browser prompts you.
2️⃣
Position your phone
Dashboard mount works best. Keep it steady.
3️⃣
Wait for GPS lock
Takes 3-10 seconds for satellite connection.
4️⃣
Drive normally
Speed updates in real-time. Toggle MPH/KM/H as needed.

Who This Tool Is For

🚗

Car Owners

Dashboard verification and calibration checks

🔧

Mechanics & Tuners

Post-mod speed verification

🏁

Off-Road Drivers

Rally and trail speed logging

🎬

Filmmakers

Chase car speed matching

🚁

Drone Operators

Follow-car footage sync

⛵

Boat Owners

Nautical speed in knots

Practical Use Scenarios

✓Calibration checks - Compare dashboard reading against GPS. Most cars read 2-5% high by design.
✓After tire changes - Different tire sizes change your effective speed. Larger tires mean your dashboard reads slower than actual.
✓Tuning verification - After ECU remaps or performance mods, verify real-world speed changes without a dyno.
✓Track day logging - Quick max speed reference without dedicated data loggers.

Speed Accuracy & Limitations

GPS speed is calculated from satellite position changes over time. At speeds above 30 km/h, accuracy is typically within 0.5 km/h. Below that, readings become less reliable.

🛰️
Satellite lock quality
More satellites = better accuracy. Open sky is ideal.
🏙️
Urban canyons
Tall buildings reflect signals and cause delays.
📱
Device chipset
Qualcomm modems tend to outperform Exynos in GPS accuracy.

Laws & Compliance

Vehicle manufacturers intentionally calibrate speedometers to read high. This is not a bug - it is legal compliance.

🇪🇺EU (UN ECE Regulation 39) - Speedometers must never indicate lower than actual. Margin: 0% to +10% + 4 km/h.
🇺🇸US (SAE J1226) - Similar guidelines. Most manufacturers add 2-5% buffer.
🇯🇵Japan (JASO) - Stricter tolerance. Typically 0% to +10%.

Real-world Validation

This tool has been field-tested across different conditions:

✓Highway testing - GPS accuracy within 1 km/h at 100+ km/h speeds
✓Urban driving - Reliable above 30 km/h. Brief signal drops in tunnels.
✓Device range - Tested on iPhone 12-15, Samsung S21-S24, Pixel 6-8
✓Dashboard comparison - Consistently shows 3-6 km/h lower than car speedometer (as expected)

Device Support

📱
iOS (iPhone/iPad)
Requires HTTPS. Safari and Chrome both work. Best on iPhone 8 and newer.
🤖
Android
Qualcomm modems perform better than Exynos. Set location mode to High Accuracy.
💻
Desktop
Tool will load but most laptops lack GPS. Speed stays at zero.

Frequently Asked Questions

How accurate is GPS speed compared to my dashboard?+

Does this work without installing an app?+

What about tunnels?+

Can police use GPS for speed enforcement?+

Does this drain battery?+

Does weather affect satellite lock?+

Safety

This tool is designed for passenger use or post-drive review. If you are the driver, set up before you start moving. Do not interact with your phone while driving.

Technical Notes

•Requires minimum 1Hz GPS update frequency
•Accuracy improves above 30 km/h
•Chipset matters: Qualcomm, Broadcom, and Apple GPS modems outperform budget chips
•Satellite count matters more than signal bars
•Assisted-GPS (A-GPS) speeds up initial lock in urban areas