Humanities › Geography Overview of Sex Ratio The Number of Males to Females in a Population Share Flipboard Email Print Adam Gault / Getty Images Geography Population Basics Physical Geography Political Geography Country Information Key Figures & Milestones Maps Urban Geography By Matt Rosenberg Geography Expert M.A., Geography, California State University - Northridge B.A., Geography, University of California - Davis Matt Rosenberg is an award-winning geographer and the author of "The Handy Geography Answer Book" and "The Geography Bee Complete Preparation Handbook." our editorial process Matt Rosenberg Updated January 28, 2020 Sex ratio is the demographic concept that measures the proportion of males to females in a given population. It is usually measured as the number of males per 100 females. The ratio is expressed as in the form of 105:100, wherein this example there would be 105 males for every 100 females in a population. Sex Ratio at Birth The average natural sex ratio for humans from birth is approximately 105:100. Scientists are not sure why there are 105 males born for every 100 females around the world. Some suggestions for this discrepancy are given as: It is possible that over time, nature has compensated for males lost in war and other dangerous activities to better balance the sexes.A more sexually active gender is more likely to produce offspring of their own gender. Thus, in a polygamous society (polygamy where one man has multiple wives), he is likely to have a greater proportion of offspring that are male.It is possible that female infants are under-reported and not registered with the government as often as male babies.Scientists also say that a woman with a slightly more than average amount of testosterone is more likely to conceive a male.Female infanticide or the abandonment, neglect, or malnutrition of female infants in cultures where males are favored may occur. Today, sex-selective abortions are unfortunately common in countries like India and China. The introduction of ultrasound machines throughout China in the 1990s led to a sex ratio of up to 120:100 at birth due to familial and cultural pressure to have one's only child as a male. Shortly after these facts became known, it became illegal for expectant couples to know the gender of their fetus. Now, the sex ratio at birth in China has been reduced to 111:100. The world's current sex ratio is somewhat on the high side – 107:100. Extreme Sex Ratios The countries that have the highest proportion of males to females are... Armenia – 115:100Azerbaijan – 114:100Georgia – 113:100India – 112:100China – 111:100Albania – 110:100 The United Kingdom and the United States have a sex ratio of 105:100 while Canada has a sex ratio of 106:100. The countries with the lowest proportion of males to females are... Grenada and Liechtenstein – 100:100Malawi and Barbados – 101:100 Adult Sex Ratio The sex ratio among adults (ages 15-64) can be highly variable and is based on migration and death rates (especially due to war). Into late adulthood and old age, the sex ratio is often highly skewed toward females. Some countries with very high proportions of males to females include... United Arab Emirates – 274:100Qatar – 218:100Kuwait – 178:100Oman – 140:100Bahrain – 136:100Saudi Arabia – 130:100 These oil-rich countries import many men to work and thus the ratio of males to females is highly disproportionate. On the other hand, quite a few countries have far more females than males... Chad - 84:100Armenia – 88:100El Salvador, Estonia, and Macau – 91:100Lebanon – 92:100 Senior Sex Ratios In later life, the life expectancy of men tends to be shorter than women and thus men die earlier in life. Thus, many countries have a very high proportion of women to men in the over age 65 range... Russia – 45:100Seychelles – 46:100Belarus – 48:100Latvia – 49:100 On the other extreme, Qatar has a +65 sex ratio of 292 men to 100 women. That is the most extreme sex ratio currently experienced. There are nearly three old men for every old woman. Maybe countries should begin to trade an over-abundance of the elderly of one gender?