We have established the 30% ratio as a bare minimum to be respected.
More specifically, the following ratios are expected:
Keynotes - 30 % women. Since the number of plenaries is small, this ratio will be more flexible.
MS (5 people): At least 2 should be women. Given that not all fields have the same representation, those finding the ratio difficult to respect, should write a report of names considered and send it to the organizing committee for approval.
http://ecm31.ecanews.org/en/speaker-policy-for-gender-balance.php