General fertility rate is a better measure of fertility than the crude birth rate because the denominator includes -

Birth rate  → Simplest indicator of fertility No. of live births per 1000 estimated mid year population  Birth rate = (No. of live birth during the year / estimated mid yr. Population) x 1000 General fertility rate  → (No. of live births in an area during the year / mid year female population (15 to 45 yrs) in the same area) x 1000. General fertility rate is a better measure of fertility than the crude birth rate because the denominator is restricted to the no. of women in the child bearing age, rather than the whole population.