Potentially quite a bit. Here's some recent data about admissions into the highly-competitive Illinois CS program: https://www.reddit.com/r/UIUC/comments/12kwc4a/uiuc_cs_admis...
Note that admissions rates for female applicants are higher across all categories—international, out-of-state, and in-state. Obviously you can't fully tell what's going on here without more of an understanding of the strengths of the different pools, but a 10–30% spread (for in-state) suggests that gender is being directly considered.
IANAL, but I'm also concerned about the degree to which this decision affects the use of other factors during college admissions. Fundamentally admissions is a complex balance between prior performance and future potential, and only admitting based on prior performance means that we're stuck perpetuating existing societal inequities.