The BBC said a peak figure of 20m - a 70% share - tuned into the corporation's coverage at the end of the service in Westminster Abbey.
More than 34 million viewers watched at least part of the BBC's TV royal wedding coverage, it added. These figures include live iPlayer viewings.
Radio figures and US TV data will be released later.Top 10
Deputy director general Mark Byford, who led the BBC's coverage, said: "We are delighted with the audience... and our programming.
"We are pleased that so many people celebrated the royal wedding with the BBC's coverage across TV, radio and online."
The BBC peak audience figure is based on estimated overnight figures.
It includes those watching BBC One, BBC One HD, the BBC News Channel and iPlayer.
According to provisional figures, there were more than 9m users of the BBC News website overall on Friday.
Police estimate a million people lined the wedding procession route from Westminster Abbey to Buckingham Palace on Friday.
The estimated figures for the BBC and ITV put the wedding in the all-time top 10 most-watched programmes, although more people watched the 1966 World Cup Final (32.3m) and Princess Diana's funeral in 1997 (32.1m).
The wedding between the Prince of Wales and Lady Diana Spencer in 1981 attracted 28.4m viewers.
Those watching the other terrestrial channels on Friday - BBC Two, Channel 4 and Five - made up only 1% of the television audience as the wedding service began.
Sky News said it had a peak of 661,000 viewers at 1100GMT, the start of the wedding ceremony, with about one million people using its website.
This post was made using the Auto Blogging Software from WebMagnates.org This line will not appear when posts are made after activating the software to full version.