Eiffel Tower sways with wind and heat

On 26 December 1999, wind gusts reached 214 km/h at the top of the Eiffel Tower, according to the official website of the monument, which recorded a swaying of 9 cm. Some sources, including RTL, suggest a swaying of 13 cm for the same day.

Eiffel Tower moves with temperature changes

On a summer day without wind, the top of the tower can move by 19 cm. The iron of the tower heats up to 60 to 70 °C and tilts away from the sun. The tower returns to its original position during the night.

Mechanism of the tower's movement

The mechanism of the tower's movement is summarized as follows: puddled iron heats up and elongates. The face turned towards the sun elongates more than the one remaining in the shade, and the tower twists. Historian and architect Bertrand Lemoine explained this on Europe 1, stating that the tower slightly curves as if it wanted to move away from the sun.

Official explanation and calculations

The official account of the tower, cited by RTL, uses a similar formula, stating that the top "flees the sun." It can thus shift up to 19 cm. As the sun moves across the sky, the illuminated face changes throughout the hours, and the curvature follows the movement. The top thus draws a curve during the day, slow and without jerks, which Bertrand Lemoine describes as imperceptible and progressive.

Heatwave impact and calculations

Le Parisien, during the heatwave at the end of June 2025, mentioned about 20 cm of movement on a day of high temperatures. The difference with the 19 cm from RTL likely lies in rounding, as the order of magnitude remains the same from one source to another. According to a calculation from The Conversation cited by the Swiss magazine Batimag, the iron of the tower can reach 60 to 70 °C when exposed to full sunlight.

Expansion and structural effects

Its coefficient of expansion approaches 12 millionths of a meter per meter and per degree. A beam of 300 m could, in theory, elongate by 36 cm for a 100 °C difference, but the structure does not heat up uniformly, which limits the actual effect. This uneven heating explains why the tower does not just grow: it tilts. The same calculation gives an expansion of 12 to 15 cm in warm seasons, with a top that slightly moves away from the sun.

Seasonal changes and temperature influence

The phenomenon also has a seasonal aspect. In winter, the tower can lose up to ten centimeters, according to Le Parisien. Between a heatwave day and a frosty morning, the Parisian silhouette therefore does not have exactly the same size. The worst storm mentioned here produced 9 cm of swaying, an ordinary summer day produces 19 cm, and the cold season removes a dozen centimeters of height.

Wind versus solar influence

Wind acts in gusts, a few seconds at a time. The sun, however, works for hours, face after face, on several hundred tons of metal. The next time a weather report announces a heatwave, the figure to remember will therefore be that of the thermometer, not that of the anemometer. One nuance remains: these 19 or 20 cm are measurements of the top, taken from one position to another, and RTL and Le Parisien recall that the tower returns to its starting position once night comes.