When first presented at the 1889 Exposition Universelle in Paris, Gustave Eiffel’s masterpiece was initially called the Tour de 300 mètres, marking the world’s tallest structure, a record it held for 41 years. Little did Eiffel know that his tower would grow ever so slightly taller each summer, breaking new records.
The wrought-iron lattice structure, fondly referred to as ‘La Dame de fer’ (the Iron Lady) by the locals, is subject to temperature-related changes; it grows in warm conditions and contracts in cold ones.
When Maurice Koechlin, Émile Nougier and Gustave Eiffel began working on their monumental project to commemorate the centenary of the French Revolution of 1789, they envisioned a monument that would serve as “an expression of France’s gratitude” and would symbolise “the art of modern engineering, the century of Industry and Science, for which the way was prepared by the scientific movement of the eighteenth century and the Revolution of 1789”.
This vision led them to give the tower a distinctly modern look, symbolising France’s position at the forefront of scientific progress and industrial achievement. The use of an iron lattice was a direct reference to materials associated with the Industrial Age.
Most solids change with temperature. Ceramics and glass expand less than metals, which in turn expand less than polymers. The reason for this lies in the behaviour of the atoms within iron. As temperatures rise, the atoms become more agitated and require more space, causing the metal to expand.
The extent to which a material expands depends on three factors: its length, the extent of the temperature change, and its natural expansion when heated.
The iron used to construct the Eiffel Tower expands slightly with temperature. For instance, a one-metre-long piece of iron expands by only a few microns for every one-degree-Celsius increase in temperature. That’s just a dozen microns – less than the thickness of a human hair. While this may seem minimal, the overall effect is significant for a structure like the Eiffel Tower, which stands 300 metres tall.
@insight_fusion_official Why Eiffell Tower Grows Taller in Summer? #tik_tok #trendingvideo #foryoupage❤️❤️ #viral_video #fyp ♬ som original – Insight Fusion
When length and temperature are added to the equation, the change becomes even more noticeable.
Temperatures in Paris, recorded over two centuries, show lows below -20 °C and highs around 40 °C. However, when metal such as the iron bars of the Eiffel Tower absorbs heat from the sun, its temperature can rise even higher than the air temperature, reaching 60 or 70 °C.
If a one-metre bar expands by 0.000012 metres when the temperature rises by one degree, then a 100-metre bar would expand by 0.12 metres if the temperature were to rise by 100 degrees. A 300-metre bar would expand three times as much: 0.36 metres, or 36 cm.
📍Paris, France
— NASA Earth (@NASAEarth) July 3, 2025
During a recent heatwave, extreme air temperatures prompted officials to close the summit of the Eiffel Tower. Land surface temperatures, collected by NASA’s ECOSTRESS instrument aboard the @Space_Station on July 1, show parts of Paris reaching more than 80°F… pic.twitter.com/BXrILLJulV
Made of over 18,000 pieces of riveted iron facing in different directions, the tower reacts differently and less radically than a single iron bar would.
According to experts, the difference in height of the tower when all these factors are considered is between 12 and 15 centimetres.
While Eiffel and his colleagues were probably aware of the thermal expansion effect when designing the tower, they lacked the atomic-level understanding we have today and could not have known to what extent their tower would grow in summer. Had they known, they might have considered completing the structure in summer to take advantage of the extra height.
