| Height (with antennas) | 330 m |
| Base | 125 × 125 m square |
| 1st / 2nd / 3rd floor | 57.6 / 115.7 / 276.1 m |
| Iron structure | ≈ 7,300 t, 18,038 parts |
| Rivets | ≈ 2.5 million |
| Person for scale | 1.7 m ≈ 1/194 of the tower |
For a 300 m iron tower, wind, not weight, governs the design. The sideways wind force on everything above a given height grows as you go down, and its overturning moment (force × lever arm) grows faster still.
Eiffel's engineers, Nouguier and Koechlin, curved the outer edges so that at any height the tangents to the profile meet where the resultant of the wind on the part above acts. The wind shear then travels straight down the inclined uprights as axial force, and the diagonals need only light bracing.
The base spreads to 125 m to give the legs a long lever arm, so overturning becomes moderate compression and tension in the leeward and windward legs. Higher up there is less tower left to catch the wind, so the profile can narrow, which gives the nearly exponential curve.
The open lattice lets most of the wind pass through. Only a small fraction of the silhouette is iron: melted down, it would form a slab only about 6 cm thick over the base. In storms the top sways only a few centimetres.
Diagram: dashed tangents from the ground, 1st and 2nd floors (● where they meet); ○ is the computed resultant of uniform wind pressure on this model, assuming 25 % lattice solidity plus the platform fronts. The 3D overlay shows the same construction on the tower.
Each leg is a box girder: four uprights (chords) at its corners, tied on every face by diagonals and horizontal struts, with internal cross-bracing diaphragms. Up close, every diagonal turns out to be a lattice girder itself, with flanges, zig-zag lacing and gusset plates.
Section cut off
Drag to orbit the leg; zoom in to reveal the lacing. Hover the legend to highlight a member type.