# Airspace

The Basics

Additional Resources

# AGL vs MSL

Altitude has many different references and definitions in aviation. The two main ones you need to know are:

**AGL** – AGL stands for “**above ground level**,” and it indicates an altitude using the ground as a reference. This is also known as absolute altitude.

**MSL** – MSL stands for “**mean sea level**“,” and it is your altitude above sea level. It’s the average height above standard sea level where the atmospheric pressure is measured in order to calibrate altitude.

**On a Sectional Chart, all of the numbers you see that denote altitudes are denoted in MSL, unless they are in parentheses.** If you see a number in parentheses, that denotes AGL.