On the eve of "wage equality day," federal statistics office Destatis revealed that one third of the difference was due to women being paid less than men for the same work.
The other two thirds resulted from the fact that women were often employed in jobs requiring fewer qualifications and responsibilities, it said.
At a regional level and in eastern Germany, the difference in wage levels was higher, at 25 percent.
In early March, with Chancellor Angela Merkel's government resisting calls to impose a quota for women in executive positions, trade union IG Metall slammed the "handicap" of being female in the labour market.
The union said it was hard for women to reconcile their professional and domestic lives owing to insufficient childcare options and because German society did not approve of working mothers.
A meeting is scheduled next week with German officials and representatives from the personnel departments of 30 major German companies to discuss the issue of woman on their management boards.