The International 5.5 Metre class was created to yield a racing keel boat giving a sailing experience similar to that of the International 6 Metre Class, but at a lower cost.

The main class regulation is a restriction on a single quantity output from a formula involving the boat's rating length L, weight (expressed as a displacement D) and sail area S; the regulation states that the output of this formula must not exceed 5.500 metres. There is considerable scope for variations in design while still meeting this restriction, and as a result each 5.5 metre boat is unique.

If the design parameters of a proposed new boat result in a formula output exceeding 5.5 metres, then one or more of the parameters must be suitably adjusted. Performance data gained from testing models towed in a long water tank (referred to in yacht design as Ship model basin) can suggest optimal combinations of parameters. The 5.5. metre rule is a variant of the International Rule (sailing) that was established already in 1907. The 5.5. is therefore closely related to larger metre boats such as the 6mR, 8mR and the 12mR.

Since 2010 the 5.5 Metre is one of the Vintage Yachting Classes at the Vintage Yachting Games.