Do women build muscle as well as men?

Short answer

In percentage terms, yes. On the same program, women grew muscle by about the same percentage of their starting size as men. Men, who start with more muscle, gained only slightly more in raw amount, and women's strength rose by a larger percentage.

Do women build muscle as well as men?
'15 times the testosterone → 15 times the muscle' — does this formula hold?
People often say women have little testosterone, so they barely gain muscle from training. We checked dozens of studies that gave men and women the same training to see how much muscle actually grew.
The starting line is clearly different
Over 15 times the testosterone, and bigger muscles
After puberty, men's blood testosterone is more than 15 times that of women. So before training, women's upper-arm muscles are about 50 to 60% as thick as men's, and their thigh muscles about 70 to 80%. Up to here, the formula is right.
But on the same training?
Muscle grew by nearly the same percentage in both sexes
An analysis that pooled 29 studies of men and women doing the same training (1,278 measurements from men, 1,537 from women) found the growth as a percentage of starting size differed by only 0.69%. An earlier analysis of 10 studies also found no sex difference in how much muscle grew.
So where is the difference?
Bigger muscles gained slightly more in raw amount
In the same analysis, men gained slightly more in raw amount. In a study of 585 men and women who trained one arm for 12 weeks, men's gain in muscle thickness was also 2.5% greater than women's. Men gained more because they started bigger, not because women's muscles responded less.
Flip side: women's strength rose faster
The percentage gain was larger in women
An analysis of 17 studies found that upper-body strength rose by a larger percentage in women than in men. In the 585-person study, men gained more strength in raw amount, but women gained more as a percentage.
Does it hold with age?
After 50, still no sex difference in percentage gain
An analysis that pooled 1,410 people over 50 found no sex difference in the percentage of muscle gained, and women's lower-body strength rose by a larger percentage. Another analysis of 1,305 people over 60 also found no sex difference in arm and leg muscle size changes.
A bigger gap than sex
On the same training, people ranged from -2% to +59%
In the 585-person study, after the same 12 weeks, muscle thickness changes ranged from -2% to +59%, and the weight people could lift changed by 0% to +250%. The gaps between individuals were far larger than the average gap between the sexes.
Bottom line: by percentage, women grow about the same
The formula breaks at the 'hormones → rate of muscle growth' link
Even though men have over 15 times the testosterone, women on the same training grew muscle by about the same percentage of their starting size as men. Men just gain a bit more in raw amount because they start with more muscle. Women can train the same way men do.