The mustard seed.

How Christianity grew from a handful of followers to about 2.7 billion people, compared with other fast-growing movements. The first three centuries are known only from models, and modern growth from counts.

Reach map Scripture translation Growth

Measured 4Model 1Estimate 1Projection tested 1Finding 1

The first three centuries: members by years since founding

Early Christians (Stark's model)Latter-day Saints (records)

Years since founding on the horizontal axis (Christianity counted from 30 CE, the Latter-day Saints from 6 April 1830). Christianity: Rodney Stark's model, 1,000 members in 40 CE growing 40% a decade (The Rise of Christianity, 1996), not counts. Latter-day Saints: the church's own membership records. On a log scale, a steady growth rate is a straight line.

1,000 to 33.9 million

Christians, 40-350 CE

Stark models 1,000 Christians in 40 CE growing 40% a decade to about 6.3 million by 300 and a majority of the empire by 350.

Model

about 6 million (about 10% of the empire)

Christians around 300 CE

Scholars put Christians at about a tenth of a Roman Empire of about 60 million by around 300 CE.

Estimate

6 to 17.9 million

Latter-day Saints, 1830-2025

From six founding members in 1830 to 17.9 million in 2025, about 43% a decade between 1850 and 1990.

Measured

64 to 267 million by 2080

Stark's 1984 projection of Latter-day Saint growth

Stark projected 64-267 million by 2080. Membership was near his high line in 2010 and near the low line by 2025, as growth slowed from about 5% a year to 1-2%.

Projection tested

558 million to 2.66 billion

Christians worldwide, 1900-2025

Christians grew nearly fivefold in 125 years but held a steady third of the world: 34.5% in 1900, 32.5% in 2025.

Measured

200 million to 2.07 billion

Muslims worldwide, 1900-2025

Muslims grew about tenfold, from about an eighth of the world to about a quarter.

Measured

about 1 million to 704 million

Pentecostals and Charismatics, 1900-2025

The renewal movement grew from under a million to about 700 million, the fastest-growing part of Christianity.

Measured

Is early Christian growth unusual?

A 40%-a-decade rate is high but not unique: a modern movement sustained it for over a century under ordinary conditions.

Finding

← All figures

Christians around 300 CE

GradeEstimate

Value: about 6 million (about 10% of the empire)
Source: Stark; Ehrman; Hopkins

The Christian case

By about 300 CE, scholars estimate, a movement that began with a crucified teacher and a few followers in Galilee had grown to about six million people. Ehrman, summarising Stark, gives "indeed 6,000,000" by 300, in an empire of "60 million people (give or take 10 million)", or "maybe 10% of the empire", and Hopkins (1998) is reported to reach a similar order of magnitude. This growth came through periods of persecution. Christians see in it the strength of the faith the first believers passed on.

What the research found

Estimate: about 6 million Christians, around a tenth of the empire, is a scholarly ballpark figure. It rests on scattered evidence, and its margin of error is about a factor of two either way: Ehrman notes that 5% or 15% of the empire are also possible.

Explore the counterarguments

No census of Christians was ever taken in the Roman Empire, so the figure is inferred, not counted, and the size of the empire itself is uncertain by about a sixth either way. Because the figure anchors Stark's growth model, any error in it changes the growth rate the model needs.