The order book for the deal reached US$15bn, the investor said. RBS held meetings and calls with UK and US investors on Tuesday.
The final pricing was inside initial price thoughts of 8.75pc.
The deal is the first AT1 from a UK bank since the country voted on June 23 to leave the European Union.
RBS is global coordinator, with Citigroup, Deutsche Bank, JP Morgan and UBS acting as joint lead managers.