The normal lapse rate is the average rate at which air temperature decreases with height in the troposphere, about 6.5 °C per kilometer of altitude (roughly 1 °C for every 150–165 m).

In simpler terms, if you climb higher in the lower atmosphere, the air usually gets cooler at this nearly steady rate under standard conditions.

This value is a long‑term average used in geography, meteorology, and aviation to estimate temperature at different heights, and it helps in understanding weather, cloud formation, and atmospheric stability.