Submit. · just now. Report Abuse. to find birth rate, you need to divide the number of new borns(in a year) on the entire population and multiply it by 1000, the unit will be: per mille; or by 100, the unit will be percent %.you do the same thing to find death rate (you divide number of deaths in one year...ubmit. · just now. Report Abuse. to find birth rate, you need to divide the number of new borns(in a year) on the entire population and multiply it by 1000, the unit will be: per mille; or by 100, the unit will be percent %.you do the same thing to find death rate (you divide number of deaths in one year...