Nine tubes acting together
SOM describes nine square tubes, each 75 feet wide, bundled into one structural system. Sharing load between tubes allows a much larger overall footprint than a single narrow tube.
THE BUILDING, IN NUMBERS
Key facts
| Architectural height | 442.1 m1,450 ft |
| Height to tip | Not confirmed |
| Highest occupied floor | Not confirmed |
| Observation deck | Not confirmed |
| Floors above ground | Not confirmed |
| Floors below ground | 3 |
| Completed | 1973 |
ENGINEERING DOSSIER
How Willis Tower works
Project evidence, construction records and the limits of what is documented. A named consultant’s role is kept separate from the architect, contractor and local engineer of record.
Why the setbacks matter
The tubes terminate at different heights. This changes the floor area as the building rises and creates its stepped silhouette. The visible form therefore records the underlying structural organisation, rather than being an independent decorative skin.
Technical source checked : SOM: Willis Tower ↗. This check covers the notes above, not every measurement in the directory.
| Topic | Recorded information | How to interpret it |
|---|---|---|
| Structural system | Nine bundled steel tubes [source] | The frame description needs to distinguish gravity support from wind and earthquake resistance. Read the engineering guide ↗ |
| Main structural material | Not confirmed | A material label does not establish steel grade, concrete strength, fire protection or connection details. Read the engineering guide ↗ |
| Basement levels | 3 [source] | Basement count does not establish pile depth, founding stratum, bearing pressure or the excavation sequence. Read the engineering guide ↗ |
| Elevator count | Not confirmed | Car count does not establish passenger capacity, speed, zoning, redundancy or peak traffic performance. Read the engineering guide ↗ |
| Construction start | Not confirmed | A start year can refer to enabling works, foundations or the main construction contract. Read the engineering guide ↗ |
| Structural topping out | Not confirmed | Topping out marks a structural milestone; facade work, commissioning and occupancy can follow later. Read the engineering guide ↗ |
Reading the vertical dimensions
The directory records 442.1 metres of architectural height. The highest occupied level has not been confirmed here. Measurement source ↗
Dividing architectural height by floor count would include the crown and any unequal floor heights. It cannot be used as a typical floor-to-floor dimension, a measure of slenderness or a structural design input.
Questions for a deeper technical review
Foundation tests, core and column sizes, construction-stage stability, creep and shortening allowances, wind-tunnel results and facade movement tolerances need project-specific evidence. Their absence here does not imply that the project lacked those studies.
SIDE BY SIDE
A sense of scale.
Height bars use the same scale. They do not represent building shape. Measurement source ↗
CHECK THE DETAILS
Sources & references
Record updated 2026-09-24. Sources can differ on height categories, floor counts and completion milestones. Read our methodology.
Explore this building
EVIDENCE & CHANGES
Verification history
Directory record updated . No dated field checks have been recorded. Updating the page does not re-verify every fact.
View 0 recorded field checks
| Checked | Field | Evidence and decision |
|---|
Correction and publication log
- : added a visible evidence register and change history. The initial evidence-register release preserved the existing measurements; subsequent corrections appear above.
- : added project-specific technical notes.
Existing source decisions and caveats
- Independent verification pending
These notes predate this visible log. Their original change dates are not reconstructed.
Earlier record edits may not have a complete audit trail. Read the methodology and correction policy ↗
QUICK ANSWERS
Common questions
How tall is Willis Tower?
Willis Tower reaches 442.1 metres (1,450 feet) by architectural height.
When was Willis Tower completed?
It was completed in 1973.
Where is Willis Tower?
Willis Tower stands in Chicago, United States.