The pulling power of David Chipperfield’s £50m transformation of the Royal Academy will be more like Herzog & de Meuron’s Tate Modern than Caruso St John’s Tate Britain, its chief executive has predicted.

Charles Saumarez Smith said he believes the RA, whose £50m transformation opens to the public on Saturday, has under-estimated the number of people who will visit just to experience the architecture.

The projection of an extra 400,000 visitors is based on the people likely to be attracted by the art and is similar to the performance of Chipperfield’s Turner Contemporary in Margate. Current RA visitor numbers fluctuate between 800,000 and a million a year.