Mont Blanc is 4,807.47 m, or 15,773 ft, above sea level at the ground survey of 2026 (Chambre des géomètres-experts de la Haute-Savoie). The Copernicus 30 m elevation model reads 4,809 m at its highest cell there.

Yes. Earlier ground surveys read 4,810.90 m in 2007, 4,806.03 m in 2019, 4,807.81 m in 2021, 4,805.59 m in 2023, against 4,807.47 m in 2026. The top is a cap of snow and ice that wind and snowfall build up or wear down from one survey to the next. The rock under it was measured at 4,789.40 m in 2026.

On the ground: surveyors climb to the top and fix its position with satellite receivers. The map on this page reads the Copernicus DEM instead, a 30 m elevation model made from satellite radar between 2011 and 2015. It gives 4,809 m at the summit, because the snow cap has moved since those radar passes and each cell averages about 30 m of ground.

At 4,807 m (15,773 ft), air pressure is about 55 % of its sea-level value in the standard atmosphere, so each breath brings in about that share of the oxygen. Altitude sickness becomes common above 2,500 m (8,200 ft) for people who come up from low ground in a day.