About this tool
The g-force meter shows how hard your car accelerates, brakes and corners – measured with your smartphone’s accelerometer. 1 g equals the gravitational acceleration of 9.81 m/s². The g-ball shows the current acceleration as a dot with the trail of the last three seconds, plus the peak values for accelerating, braking and both cornering directions.
At the start the tool measures the direction of gravity while standing still. From it, it derives the car’s axes – whether the phone sits upright in a holder or lies flat. All values are processed in your browser only.
How it works
- Mount the phone firmly: upright in a holder with the screen towards you, or flat with the top facing forward.
- With the car standing still, tap “Start” and allow access to the motion sensors. Calibration takes less than a second.
- Drive and watch the g-ball and the peak values. After repositioning the phone, tap “Set zero”.
Frequently asked questions
Which values are normal?
In everyday driving you mostly stay below 0.3 g. Emergency braking with ABS reaches about 0.8 to 1 g on a dry road, and normal cars manage similar values in corners. Sports cars on a track go beyond. How the deceleration affects the braking distance is shown by the Stopping Distance Calculator calculator.
Why does the meter not show exactly 0 when standing?
If the car stood on a slope during calibration or the phone moves in its holder, a small offset remains. Park on level ground and tap “Set zero”. Uphill and downhill, part of the slope shows up as longitudinal acceleration.
How accurate is it?
Phone sensors are built for games and screen rotation, not for measurement. The accuracy is good enough to compare drives; absolute values may be off by a few hundredths of a g. The tool smooths vibrations with a low-pass filter.
Does it work on iPhone?
Yes. Safari asks for permission for motion and orientation on start – tap “Allow”. Check whether your device delivers the sensors with the Sensor Check. Measure your acceleration times with the 0–100 Acceleration Timer.