Eiffel Tower Gets Taller in the Heat? Here What You All Need to Know

The Eiffel Tower, known initially as the “Tour de 300 meters,” is far more than a historic landmark built for the 1889 World’s Fair, this iron structure was designed to showcase French engineering excellence. However, what many don’t know is that this iconic Parisian monument actually grows taller during the summer months and its shocking.

Due to thermal expansion, the tower can increase in height by up to 15 centimeters when temperatures rise. Engineers planned it as a lightweight, yet stable structure capable of withstanding wind and weather but even they knew iron couldn’t escape the laws of physics.

Designed for Height and Strength

Engineers Maurice Koechlin and Émile Nougier first proposed the 300-metre tower to Gustave Eiffel. Eiffel selected puddled iron for the construction a material both familiar and resilient under stress. It allowed the structure to stay light and safe from strong wind forces and weighing 7,300 tonnes, the tower contains nearly the same weight in air—about 6,300 tonnes—showing its impressive lightness despite its massive size.

How Thermal Expansion Works

Thermal expansion explains the phenomenon. As temperatures rise, atoms in solids agitate more, increasing the distance between them and this leads materials to grow. Engineers know that different materials expand at different rates. Ceramics and glasses expand the least, followed by metals, and then polymers, which expand the most.

Measuring Growth in the Eiffel Tower

The iron in the Eiffel Tower has a thermal expansion coefficient of 12×10⁻⁶ per °C. So, for every one-degree rise in temperature, a metre of iron grows by about 12 microns—thinner than a human hair. Now consider the Eiffel Tower’s 300-metre height and a 100°C temperature variation between winter and summer. That results in a vertical expansion of up to 36 centimeters. In reality, specialists have measured the growth at around 12 to 15 centimeters.

A Giant Iron Thermometer

Because sunlight heats only one side more than the others, the tower doesn’t just grow; it bends slightly away from the sun. This makes it not only an architectural marvel but also a functional thermometer. As temperatures change, so does its size—proof of the dynamic nature of even the most solid structures.