The Eiffel Tower grows about 15 centimeters taller in summer.

Thermal expansion happens because a material's average atomic spacing changes as temperature rises. In the tower's iron framework, tiny changes along many structural members can alter the dimensions of the whole structure. The atoms do not grow larger, and the structure is not adding new metal; its existing material occupies slightly different dimensions.

Actual movement depends on the temperature of the metal, not simply the season printed on a calendar. Sunshine, shade, wind and recent weather affect that temperature. The structure is also a lattice rather than a single vertical rod, so a basic expansion calculation illustrates the scale without predicting the measured motion of every part.

Uneven heating adds another effect. Sunlit iron can expand more than shaded iron, making the summit move sideways, generally away from the Sun. A sideways displacement, a circular daily path and an increase in vertical height are not interchangeable measurements. The familiar 15-centimeter number should therefore always be attached to a specific explanation.

The Eiffel Tower's official operator explains that its metal structure changes size as temperatures vary. Its article on changing size describes small seasonal dimensional changes and tilting produced by sunlight. That supports the underlying fact of thermal movement, but not a promise that every summer brings one particular height increase.

In a separate technical history article, the operator describes the summit tracing a roughly circular curve about 15 centimeters in diameter over a day. The explanation is successive heating of different sides as the Sun moves. This is an especially useful correction because a diameter of motion is not additional vertical height.

The tower was inaugurated in 1889, and later antenna installations permanently changed its overall height. Its official total height became 330 meters with the antenna addition in 2022. Permanent additions belong in the history of the structure, while thermal expansion is a reversible response occurring without construction work.

Engineers distinguish these processes when describing structural behavior. They also distinguish thermal movement from wind-induced motion, which has another cause and varies with wind conditions. A single headline about the tower "growing" can otherwise merge construction, heating and bending into an apparent measurement that means several different things.

A simple classroom calculation multiplies original length, temperature change and a material's thermal-expansion coefficient. For a long iron member, an ordinary weather-related temperature change can produce measurable expansion. But a real tower includes angled members, connections and temperature gradients, so applying that formula to its total advertised height is only an illustration.

Thermal movement is normal engineering behavior, not evidence that the tower is about to fail. Designers accommodate changes in dimensions and forces rather than assuming structures never move. Similar reasoning appears in bridge bearings and other connections that permit controlled movement. The meaningful question is whether movement remains within the conditions the structure can accommodate.

A useful comparison is a bridge joint: engineers expect metal dimensions to vary and provide ways to accommodate movement. The tower makes the same material behavior visible on a famous structure, but its open framework distributes expansion through many connected members rather than one isolated bar.