Almost every map says 4,810 metres. At the survey in September 2023 the surveyors arrived at 4,805.59. And take the snow away and the rock sits at roughly 4,792.
Three different numbers for the same mountain, and none of them is invented. The difference comes down to the fact that the highest point of Mont Blanc is not stone. It is a dome of snow, and it changes.
The survey made every two years
Since 2001 the summit has been surveyed regularly by surveyors from the Haute-Savoie department, always in mid-September. It is a fairly unusual arrangement: an expedition with ropes, guides and measuring equipment that climbs the mountain purely to establish a number.
Around twenty people in eight rope teams took part in the 2023 survey, and for the first time a drone was used alongside satellite positioning. The accuracy of the measurement itself is given as a matter of a few centimetres.
The result was 4,805.59 metres, which was 2.22 metres lower than at the 2021 survey, when the summit measured 4,807.81 metres.
What varies is the wind, not the mountain
It is tempting to read every drop as a climate alarm, but the surveyors themselves are careful there. The snow dome on the summit is built up and blown off by high-altitude winds, and how much snow is sitting there in a given week in September depends mostly on precipitation and wind direction over the preceding year.
The rock beneath is effectively unchanged. It sits at around 4,792 metres, and it is also some forty metres west of the snow-covered high point. Anyone standing on the summit of Mont Blanc is therefore not standing on the mountain's highest rock.
Why 4,810 is still there
4,810 is not a measurement but an established map value. It is the figure in school atlases, on hiking maps and on signs in Chamonix, and it has stayed the same for so long that it has become the mountain's second name.
It is also the figure we engrave. A nameplate is not a measurement series, and swapping the number every two years would make a piece dated rather than lasting. How elevations are calculated at all, and why the zero level is harder than it sounds, is covered in the article on measuring height.
Whose summit is it?
A side question that has never really been settled: the border. France counts the entire summit as French, while Italy holds that the border follows the watershed and therefore splits the summit between the two countries. The question has been open since the nineteenth century and has no practical consequences, but it explains why Italian and French maps can look different in that particular corner.
The massif is the point, not the peak
Building the Mont Blanc relief made one thing obvious: the summit itself is the least interesting thing in the frame. What carries the image is the glaciers running north towards the Chamonix valley, the ridges between them, and the elevation difference from the valley floor up to the dome.
The massif also has so much elevation range of its own that the relief needs almost no vertical scaling to read at a distance. That is unusual. Most places need help, which we have written about in the piece on vertical exaggeration.
If you want the mountain on your wall, the Mont Blanc piece comes in oak or black, with or without a nameplate.