The float printing options that ship with Erlang all suck. You either don't have sufficient precision, or you have an extremely verbose representation: 1> io:format("~w ~.18g ~g ~s~n", [0.1234567, 0.1234567, 0.1234567, float_to_list(0.1234567)]). 0.123457 0.123456700000000003 0.123457 1.23456700000000002548e-01 2> io:format("~w ~.18g ~g ~s~n", [0.1, 0.1, 0.1, float_to_list(0.1)]). 0.100000 0.100000000000000006 0.100000 1.00000000000000005551e-01 mochiweb includes an implementation of the algorithm from the "Printing Floating-Point [...]