We classify definable linear orders in o-minimal structures expanding groups. For example, let (P, (sic)) be a linear order definable in the real field. Then (P, (sic)) embeds definably in (Rn+1, <(lex)), where <(lex) is the lexicographic order and n is the o-minimal dimension of P. This improves a result of Onshuus and Steinhorn in the o-minimal group context.