A Norwich library voted the UK's busiest has been expanded to cope with the extra visitors.
Norfolk and Norwich Millennium Library in The Forum, was named as the UK's busiest for the second time in March.
A spokesman for Norfolk County Council said users had complained the ground floor felt cramped.
Improvement work has been carried out to provide an extra 177 sq ft (16.44m sq) including a back office area being opened up to make part of the library.
The county council has also installed a new smaller customer service desk and self-service machines, to create more space.
Jennifer Holland, head of libraries at Norfolk County Council, said: "I am really pleased that we have been able to improve the library in this way.
"The latest changes have provided a huge amount of additional space, which I'm sure will be welcomed by the thousands of people who visit us every week."
The Norfolk library attracted 1,500,695 visitors and lent 1,139,090 books in 2007/2008.