What is the Gini coefficient? Measuring inequality

The Gini coefficient is a single number that measures how unequally something, usually income, is shared across a population. It runs from 0, where everyone has exactly the same, to 1, where one person has everything. The World Bank and others often write it from 0 to 100 instead, so a Gini of 0.35 and a Gini index of 35 mean the same thing.

In short

• The Gini comes from the Lorenz curve: the further the curve sags below the line of perfect equality, the higher the number.
• Most countries score between about 0.25 and 0.55 for income, with Northern and Central Europe at the low end and southern Africa and Latin America at the high end.
• One number hides a lot: the same Gini can describe very different societies, and figures differ by data source, year and whether they measure income or spending.

Where does the Gini coefficient come from?

The Italian statistician Corrado Gini proposed the measure in 1912. It builds on a chart the American economist Max Lorenz drew a few years earlier, now called the Lorenz curve. Line everyone up from poorest to richest. On the horizontal axis, mark the share of people counted so far; on the vertical axis, the share of total income they hold between them.

If incomes were perfectly equal, the poorest 20% would hold 20% of income, the poorest 50% would hold 50%, and the curve would be a straight diagonal line, the line of equality. In any real economy the poorest 20% hold less than 20%, so the curve sags below the diagonal. The Gini coefficient is the area between the line of equality and the Lorenz curve, divided by the whole area under the line. In the notation Our World in Data uses, if A is the gap and B the area under the curve, the Gini is A divided by A plus B.

How do you calculate a Gini coefficient? A worked example

Take a village of five people who earn, in a year, $10,000, $20,000, $30,000, $40,000 and $100,000. Total income is $200,000.

Step 1: work out each person's share of the total, poorest first: 5%, 10%, 15%, 20% and 50%.

Step 2: add them up as you go, to get the Lorenz curve's points. After one person, 5% of income; after two, 15%; after three, 30%; after four, 50%; after all five, 100%. So the poorest 80% of the village earn half its income.

Step 3: find B, the area under that curve. Each person is one-fifth, or 0.2, of the horizontal axis, and the area of each slice is its width times the average of its two heights: 0.2 × (0 + 0.05) ÷ 2, then 0.2 × (0.05 + 0.15) ÷ 2, and so on. The five slices add up to 0.30.

Step 4: the whole triangle under the line of equality has an area of 0.5. So A, the gap, is 0.5 − 0.30 = 0.20, and the Gini is 0.20 ÷ 0.5 = 0.40.

Now move $20,000 from the richest person to the poorest, so incomes are $20,000, $30,000, $30,000, $40,000 and $80,000. Run the same steps and the Gini falls to 0.26. Nobody's income was created or destroyed; only its spread changed. That is what the number tracks.

How do countries compare?

The table below shows the World Bank's latest income or consumption Gini index for a sample of countries, as listed in its data in November 2026. Each comes from a household survey in the year shown, so the years differ.

Country	Gini index	Survey year
Slovak Republic	23.8	2023
Norway	26.5	2023
United Kingdom	32.4	2021
Germany	33.7	2022
China	36.0	2022
United States	41.8	2024
Brazil	50.3	2024
South Africa	54.1	2022
Colombia	54.4	2024
India	23.0	2023

India is set apart on purpose. Its figure, like many lower-income countries' in the World Bank's data, measures consumption, what households spend, rather than income. Spending is more equal than income, because rich households save much of what they earn, so a consumption Gini of 23 cannot be read against an income Gini of 24 in Slovakia as if they were alike.

Other sources give other numbers for the same country. The US Census Bureau, for example, measures household income before taxes, and its annual report found inequality "not significantly different" between 2023 and 2024. Any Gini quoted without its source and year is hard to use.

What does the Gini coefficient miss?

It compresses a whole distribution into one number, so different societies can share a score. A country where the poorest are very poor but the rest are alike, and one where the middle is equal but a few at the top are very rich, can land on the same Gini.

It is also more sensitive to changes in the middle of the distribution than at the very top. Our World in Data shows that the share going to the richest 1% can rise substantially while the Gini moves only a little. That is why researchers also quote top income shares, or the ratio between the 90th and 10th percentiles.

It depends on what is measured. Income before taxes and benefits is more unequal than income after them; wealth, what people own, is far more unequal than income, and debts can push a wealth Gini above 1. And it says nothing about why incomes differ, whether people move up and down over their lives, or how rich the country is overall. A poor country and a rich one can have the same Gini, which is why it is read alongside measures such as GDP per person.

Still argued

The Gini measures inequality; it doesn't say how much is too much. Some economists and political thinkers hold that high inequality weakens growth, health and trust, and that taxes and transfers should narrow it. Others argue that what matters is how well off the poorest are and how freely people can move up, not the gap itself, and that rewards for work and risk are what make market economies grow. Supporters of socialism go further, seeing inequality as built into private ownership. The evidence on the links between inequality and growth is mixed and depends on the country and period studied.

Why does it matter for the reader?

When a headline says inequality rose or fell, the Gini is usually the number behind it. Knowing how it is built lets a reader ask the right questions: income or consumption, before or after taxes, which survey and which year. It is one of the basic tools of economics, useful for comparing places and tracking change over time, as long as nobody mistakes it for the whole picture.

Check yourself

• Describe a Lorenz curve to a friend: what is on each axis, and why does it sag below the diagonal?
• In the five-person example, why did moving $20,000 from the richest to the poorest lower the Gini so much?
• Why can't India's Gini be compared directly with Slovakia's, and what other measures fill the Gini's gaps?

Sources

• Gini index (SI.POV.GINI) — World Bank, Poverty and Inequality Platform
• Poverty and Inequality Platform — World Bank
• Measuring inequality: what is the Gini coefficient? — Our World in Data
• Income in the United States: 2024 — U.S. Census Bureau, 2025