There is no sea level on Mars. Heights are measured from the areoid. The NASA fact sheet gives 6.36 mbar at the mean radius and a scale height of 11 km. A useful first screen is an isothermal atmosphere: pressure at elevation z is the datum pressure times exp(-z / H), with z positive upward. [1]
That curve is not the weather. At the mean radius the same fact sheet lets pressure run from 4.0 mbar to 8.7 mbar through the year, because carbon dioxide freezes and thaws. Dust and local slope move it again. Use the curve to see that a high site and a basin are different machines. Then read a climate model or a lander record for the site you mean.
Screen
The buttons mark the datum, 7 km below it, and 22 km above it. Seven kilometers is a round depth, not the floor of Hellas, which is deeper. Twenty-two kilometers is the round height used for the summit of Olympus Mons above the datum. The density line uses the temperature you type. The fact-sheet average, 214 K (-59 C), is the default, and the fact sheet's surface density is about 0.016 kg per cubic meter, with a wide uncertainty. [1]
Class B instrument
H and P_datum are the fact-sheet scale height and the 6.36 mbar mean-radius pressure. The seasonal swing, about 4.0 to 8.7 mbar at the mean radius, is not in this curve. Hellas is deeper than 7 km. The 7 km button is a round screen, not a survey of the basin floor.
Why a designer cares
Landed elevation is an entry problem and a breathing problem at the same time. Thinner air means a heavier lander has less help from a parachute, and a surface suit or a habitat inlet sees less ambient pressure. The Cabin gas page starts from a pressure you choose. This page only tells you what the ambient screen is. Atmosphere of Mars holds the composition.
See also
What links here
References
- NASA Goddard Space Flight Center. Mars Fact Sheet. Pressure, scale height, mean molecular weight, and temperature. Updated 19 May 2025. https://nssdc.gsfc.nasa.gov/planetary/factsheet/marsfact.html