The dollars raised tell you how big a deal is, not how much of the company actually changed hands. Line the two up and a pattern appears: the larger the raise, the thinner the slice. The two biggest IPOs ever, SpaceX and Saudi Aramco, sold the least of themselves — roughly 4% and under 2%.
Record raises, thin slices
Float = capital raised divided by market cap at the offer price. Saudi Aramco (2019) placed $29.4B on a $1.7T base for the thinnest slice any mega-IPO ever sold: 1.7%. SpaceX (2026) is the largest IPO in history by dollars — ~$86B raised on a $1,770B cap — yet floats just 4.2%, the second-thinnest ever: scarcity by design. The widest floats belong to motivated sellers: AIG offloading over half of AIA (~58%) in 2010 as a forced post-crisis seller, and the U.S. Treasury exiting GM at 37% in 2010. A typical IPO floats 5–10% to retail; historic mega-listings, 15–40%, with the usual mega-listing selling about a fifth of itself. The records sold least.
Key findings
- Saudi Aramco holds the thinnest slice of any mega-IPO — $29.4B placed on a $1.7T base for a 1.7% float.
- SpaceX is the largest IPO ever by dollars (~$86B) yet floats just 4.2% — the second-thinnest slice on record.
- The widest float belongs to AIA Group at ~58%, as AIG offloaded over half the company in 2010; typical mega-listings sell about 20%.