China’s 2020 census counted 17.52 million more men than women in the 20-to-40 age group alone: 214.37 million men against 196.85 million women, a sex ratio of 108.9 in that cohort. Globally, an estimated 142 million girls are considered “missing” as a result of gender-based sex selection, according to UNFPA, with India alone estimated to account for roughly 46 million of the global missing-women total, per research building on economist Amartya Sen’s foundational 1990s analysis of the phenomenon.
These are not abstract statistics: they represent tens of millions of real demographic imbalances working their way through national populations, with consequences for marriage markets, migration, and social stability that will play out over decades.
What Is the Population Sex Ratio?
The population sex ratio is most commonly expressed as the number of males per 100 (or per 1,000) females in a population, though the reciprocal measure, females per male, is also used in some contexts. Because this ratio varies substantially by age group within the same country, demographers rarely rely on a single national figure alone, instead examining ratios separately at birth, in childhood, at working age, and at older ages, each of which tells a different part of the story.
Why Sex Ratios Differ Naturally by Age
Even with no human intervention whatsoever, sex ratios shift systematically across the life course. Slightly more boys than girls are born in virtually every human population, a biologically normal pattern that demographers place in a range of roughly 102 to 107 boys per 100 girls, reflecting a consistent, cross-culturally universal biological baseline.
From that point, male mortality rates exceed female mortality rates at nearly every age, gradually narrowing and eventually reversing the ratio, such that by older ages, women substantially outnumber men in most populations, a pattern explored in detail in coverage of the global population living alone, where older women’s higher survival rates are a primary driver of solo living in advanced age.
Where Are Male Surpluses Found?
China and India together account for the largest documented national sex ratio imbalances in the world. China’s 2024 estimated sex ratio stood at 1.09 males per female at birth and 1.04 overall, with the ratio actually inverting among the 65-and-older population, where women outnumber men (0.86 males per female), consistent with the universal pattern of higher male mortality at older ages.
India’s overall sex ratio was estimated at 1.06 males per female in 2023, with a birth ratio of 1.1 and an under-15 ratio of 1.11, though India’s aggregate national ratio has shown some improvement in recent estimates after decades of decline, moving from roughly 943 females per 1,000 males in 2011 toward an estimated 944 females per 1,000 males (equivalently 1.06 males per female) by 2023.
Sex Ratios by Age Group, China and India
| Country | At Birth | Under 15 | Working Age (15–64) | 65+ |
|---|---|---|---|---|
| China (2024 est.) | 1.09 | 1.14 | 1.06 | 0.86 |
| India (2023 est.) | 1.10 | 1.11 | 1.07 | , (data limited) |
Source: national statistical estimates compiled via Demographics of China / Demographics of India reference data, 2023–2024.
Total Population Sex Ratio, Selected Countries Worldwide (Males per Female)
| Country | Total Sex Ratio | Context |
|---|---|---|
| Bahrain | 1.50 | Extreme male skew from migrant labor force |
| India | 1.06 | Historically elevated, linked to son preference |
| Algeria | 1.03 | Near global average |
| China | 1.04 | Historically elevated, declining in recent birth cohorts |
| World (average) | 1.01 | Global baseline |
| United States | 1.01 | Close to global average |
| Azerbaijan | 1.00 | Near parity overall despite high birth ratio |
| Australia | 0.99 | Near parity |
| Mongolia | 0.99 | Near parity |
| Peru | 0.99 | Near parity |
| Canada | 0.99 | Near parity |
| Argentina | 0.98 | Slight female majority |
| Albania | 0.97 | Slight female majority |
| Austria | 0.96 | Female majority, older population structure |
| Bangladesh | 0.96 | Female majority |
| Angola | 0.96 | Female majority |
| Moldova | 0.85 | Large female majority, linked to male emigration |
| Russia | 0.87 | Large female majority, linked to male mortality gap |
| Hong Kong | 0.82 | Lowest documented globally, linked to female-dominated migration |
Source: CIA World Factbook, 2024 estimates, compiled via Wikipedia “List of countries by sex ratio”; national census data for China and India.
Sex Ratio at Birth Versus Overall Population Sex Ratio
This distinction is central to interpreting sex ratio data correctly. The sex ratio at birth (SRB) captures only the ratio among newborns in a given year and is the most direct measure of sex-selective practices, since it is least affected by migration or differential mortality accumulated over decades.
The overall population sex ratio, by contrast, reflects the cumulative effect of decades of birth ratios, migration flows, and mortality patterns layered on top of each other, meaning a country can show a roughly normal current SRB while still carrying a substantial overall population imbalance inherited from decades of historically skewed birth ratios, as China’s data illustrates: its SRB has been declining from a peak but its working-age population still reflects the much higher historical ratios recorded in the 1990s and 2000s (up to 121.21 in the 2010 census by some measures).
Why Do Persistent Imbalances Develop?
Research attributes sustained sex ratio imbalances, where they occur, to several interacting factors, with son preference and sex-selective practices the most extensively documented drivers in South and East Asia specifically:
- Sex-selective practices, enabled by the spread of prenatal sex-determination technology beginning in the 1980s and 1990s, identified by researchers as a primary driver of China and India’s sharply elevated child sex ratios during that period.
- Son preference, a documented cultural pattern in parts of South and East Asia rooted in kinship structures, inheritance customs, and old-age support expectations, which researchers link directly to the demand for sex selection.
- Differential postnatal care and excess female mortality, identified alongside sex-selective abortion as contributing to India’s estimated “missing women,” per research building on the Sen framework.
- Migration, which can create substantial regional or local sex ratio imbalances even in countries with a roughly normal national birth ratio, as labor migration often skews heavily toward one sex in origin or destination communities.
- Age structure effects, since a historically skewed birth cohort continues to show elevated male representation in official statistics for decades as that cohort ages, independent of any current-year birth ratio.
Notably, some researchers caution that historical SRB and “missing girls” figures for China specifically may have been overestimated due to data quality issues in earlier censuses, with the 2020 census, assessed as substantially more accurate due to improved data collection methods, showing some moderation relative to peak historical estimates, illustrating the importance of data quality caveats in this research area.
How Sex Ratios Affect Marriage Markets
A sustained surplus of men relative to women in marriage-age cohorts is documented by demographers as contributing to a “marriage squeeze”, a structural shortage of potential brides relative to the number of men seeking marriage within a similar age range, a dynamic examined in more depth in coverage of marriage market demographics.
Research modeling skewed sex ratios in China and India projects this marriage squeeze intensifying through mid-century as the large, historically male-skewed birth cohorts of the 1990s through 2010s reach peak marriage age, though the size and timing of the effect depends on assumptions about future sex ratio trends and marriage age patterns that remain genuinely uncertain.
Social and Economic Consequences
UNFPA and academic research have documented a range of social and economic consequences associated with persistent sex ratio imbalances beyond marriage market pressure, including elevated risks of human trafficking of women into regions with marriage squeezes, and broader social effects tied to large populations of unmarried men, sometimes termed a “structural surplus of grooms” in demographic literature examining China’s marriage market specifically. These consequences are documented as associated patterns in the research literature rather than deterministic, guaranteed outcomes of any given sex ratio imbalance.
What Happens as Imbalanced Cohorts Age?
Because a sex ratio imbalance recorded at birth persists as that birth cohort ages through the population, subject to modification by mortality and migration, the marriage-age imbalance associated with peak historical SRB years (China’s 2000 and 2010 census data showing SRBs of 119.92 and 121.21, well above the normal biological range) will continue moving through China’s population structure for decades, even as more recent birth cohorts show improving, more normalized ratios. This cohort effect means the social and marriage market consequences of historically elevated SRBs are, to a significant degree, already locked in for the cohorts affected, regardless of subsequent policy change.
Can Sex Ratios Return Toward Balance?
Evidence from both China and India shows measurable, if gradual, improvement in more recent birth cohorts relative to the peak imbalance years. China’s SRB declined from a 2010 census figure of 121.21 to 111.30 by the 2020 census, still above the normal biological range but a meaningful reduction. India’s estimated annual missing female births at birth similarly declined across the 2001–2012 to 2007–2012 measurement periods, according to UNFPA-commissioned research.
Both countries have implemented policy measures, including restrictions on medically unnecessary sex-selective procedures and public campaigns targeting son preference, that researchers credit with contributing to this moderation, though both countries’ sex ratios generally remain above the normal biological range as of the most recent available data.
Conclusion
Population sex ratios carry real demographic weight precisely because they compound over time: a skewed birth cohort does not correct itself quickly, but instead moves through decades of marriage-age, working-age, and eventually elderly-age statistics, shaping marriage markets and social structures long after the birth ratios that produced it have moderated.
China and India’s gradual but still incomplete progress toward more balanced sex ratios at birth, alongside the tens of millions of people already born into historically skewed cohorts, means the demographic consequences of past sex ratio imbalances will continue working through these populations for decades, regardless of how quickly current birth ratios normalize.
Key Findings
- China’s 2020 census recorded 17.52 million more men than women in the 20-to-40 age group, with a sex ratio of 108.9 in that cohort.
- An estimated 142 million girls are considered “missing” globally due to gender-based sex selection, according to UNFPA, with India alone estimated to account for roughly 46 million of that total.
- China’s sex ratio at birth declined from a 2010 census peak of 121.21 to 111.30 by 2020, improvement, but still above the normal biological range of 102–107.
- Sex ratios invert with age in every studied population: China’s 65-and-older sex ratio is 0.86 males per female, reflecting higher male mortality, compared with 1.09 at birth.
- India’s overall population sex ratio was estimated at 1.06 males per female in 2023, with a birth ratio of 1.1 and an under-15 ratio of 1.11.
- Globally, total population sex ratios range from 1.50 males per female in Bahrain (driven by migrant labor) down to 0.82 in Hong Kong, illustrating how far individual countries can deviate from the world average of 1.01.
- Research modeling projects marriage squeeze effects in China and India intensifying through mid-century as historically male-skewed birth cohorts reach peak marriage age.
Frequently Asked Questions
1. What is a normal population sex ratio?
At birth, demographers consider roughly 102 to 107 boys per 100 girls biologically normal; this ratio naturally declines with age in every population due to higher male mortality, typically inverting to a female majority at older ages.
2. Why do some countries have more men than women?
Documented drivers include sex-selective practices tied to son preference, differential postnatal care and mortality, migration patterns, and the cumulative effect of historically skewed birth cohorts aging through the population.
3. Does having more men than women affect marriage?
Yes, demographers document a “marriage squeeze” effect where sustained male-skewed sex ratios in marriage-age cohorts create a structural shortage of potential partners, a dynamic examined further in coverage of marriage market demographics.
4. What is the sex ratio at birth?
It measures the ratio of male to female births in a given year, the most direct indicator of sex-selective practices, as distinct from the overall population sex ratio, which reflects decades of accumulated birth ratios, mortality, and migration.
5. Which countries have the largest male surplus?
China and India show the largest documented national imbalances, with China’s 2020 census counting 17.52 million more men than women aged 20–40, and India’s national ratio at 1.06 males per female as of 2023.
6. Can a sex imbalance disappear over time?
Both China and India show measurable improvement in more recent birth cohorts relative to peak imbalance years, though the demographic effects of historically skewed cohorts persist for decades as those cohorts age through the population.
7. Is “more men than women” always evidence of sex selection?
No, migration and age structure can produce substantial sex ratio differences even where the underlying sex ratio at birth is normal; researchers specifically distinguish birth-ratio evidence from broader population-level imbalances for this reason.
8. How is “missing women” estimated?
Researchers, building on economist Amartya Sen’s framework, estimate missing women by comparing observed sex ratios against expected biologically normal ratios and mortality patterns, attributing the gap to sex-selective abortion, differential care, and excess female mortality.
9. Do sex ratios vary by age within the same country?
Substantially. China’s 2024 data shows a sex ratio of 1.09 at birth, 1.14 under 15, 1.06 at working age, and 0.86 among those 65 and older, illustrating how much the ratio shifts across the life course within a single population.
10. What social consequences are associated with male-surplus populations?
Research documents associations with marriage squeeze effects, elevated trafficking risk in some contexts, and broader social effects tied to large populations of unmarried men, though these are documented as associated patterns rather than certain outcomes.
Sources
- UNFPA China, “Every Girl Counts: South-South Dialogue to End Gender-based Sex Selection,” 2023.
- United Nations Population Fund (UNFPA) India / Office of the Registrar General, “How many girls are missing at birth in India?”
- “Unmatched: From Skewed Births to a Structural Surplus of Grooms” (China marriage market research), arXiv, 2026.
- Mei, L. & Jiang, Q., “Overestimated SRB and Missing Girls in China,” Frontiers in Sociology, 2021.
- UNFPA China, “The Challenge of Normalizing Sex Ratio at Birth in China: A Long-Term Endeavor,” Policy Brief, 2024.
- Guilmoto, C.Z., “Skewed sex ratios at birth and future marriage squeeze in China and India, 2005–2100,” Demography, 2012.
- United Nations, Department of Economic and Social Affairs, Population Division, “Sex ratio at birth,” World Population Prospects 2024.
