SDL_STANDARD_GRAVITY - Man Page

#include <SDL3/SDL_sensor.h>

#define SDL_STANDARD_GRAVITY    9.80665f

The accelerometer returns the current acceleration in SI meters per second squared. This measurement includes the force of gravity, so a device at rest will have an value of SDL_STANDARD_GRAVITY away from the center of the earth, which is a positive Y value.

This macro is available since SDL 3.2.0.