How big is Willis Tower?
Willis Tower: 442 m (1,450 ft). Measured as height — to the roof (527 m with antennas).
Source: Wikipedia — Willis Tower
Where it sits
Among the 23 buildings & towers on this page Willis Tower ranks 12th from the top by size. The largest in the group is Burj Khalifa at 828 m, which is 1.87× the size of Willis Tower, while the smallest, Christ the Redeemer, is 30 m.
Stand an adult of 1.7 m beside it and the ratio is 260×: you would need 260 people stacked head to foot to match its size.
In everyday distances
A football pitch is about 105 m long. Willis Tower is 4.21× that, which puts it at 4.2 pitch lengths from end to end.
Walking at an easy 1.4 m/s you cover 442 m in 5.3 minutes. A jet at 900 km/h covers it in 1.8 seconds.
Next to its neighbours in size
The nearest thing larger than it in this collection is Empire State Building at 443 m (1,454 ft), 1× the size. Both figures are the same kind of measurement, so the gap is a fair one.
The nearest thing smaller is Emma Maersk at 397 m (1,302 ft), so Willis Tower is 1.11× as big as it. They come from different groups — vehicles & ships against buildings & towers — which is what makes the pairing interesting.
Against fixed yardsticks
Against three fixed yardsticks — Willis Tower is 1.34× the size of Eiffel Tower (330 m); Willis Tower is 14.8× the size of blue whale (29.9 m); Earth (12,742 km) is 28,822× the size of Willis Tower.
How this figure was taken
Building heights depend on the rule used: architectural height counts spires but not antennas, tip height counts everything. The basis is named with each figure.
How the sizes are taken. Each figure says what it measures — height, length, diameter or elevation — and for which individual or convention. Everything is drawn standing upright on one baseline so a single scale holds, including things that are long rather than tall. Values come from the linked Wikipedia article for each item.
Read the rest — common questions
How big is the Willis Tower?
442 m (1,450 ft), measured as height: to the roof (527 m with antennas).
Where does the Willis Tower rank among buildings & towers?
Number 12 of 23 on this site, from Burj Khalifa at 828 m down to Christ the Redeemer at 30 m.
What is the next size up?
Empire State Building, at 443 m, is 1× the size.
What is the next size down?
Emma Maersk, at 397 m, is 1.11× smaller.
How reliable is the figure?
It is taken from the cited Wikipedia article and states its basis (to the roof (527 m with antennas)). Values are rounded, and where individuals differ the figure is a representative one, so expect small differences from other sources.