I presume you ask about the minimum height when a hill is considered a mountain. In the UK it's 2000 feet.
The height of a mountain peak above sea level is called its elevation.
546
elevation
700 meter
While Chimborazo is not the tallest mountain by height above sea level, With an elevation of 6268 m, Chimborazo is the highest mountain in Ecuador.
The summit of K2 is 8611 metres above sea level
Macgillycuddy's Reeks - the height is 1,038 metres above sea level.
A mountain top is higher (greater) in altitude. That is the definition of altitude : height above a surface, or above sea level.
The tallest mountain in Australia, Mount Kosciuszko reaches a height of 2228 meters (7310 ft) above sea level.
We call this "elevation".
I presume you ask about the minimum height when a hill is considered a mountain. In the UK it's 2000 feet.
At the top. "Altitude" means elevation or height above a surface, or above sea level.