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More on Numbers of Converts

In case you didn’t read the post of yesterday, I include the final two paragraphs here.  Skip them if you remember what I said.  The issue I’m dealing with is how much and how fast did the Christian church grow over the first four centuries.   I would very much like your feedback, and if you’re a numbers person, I would love it if you would check my calculations to see if I’m making any egregious errors.   All of this is lifted, again, from a rough draft of ch. 6 of my book on the Christianization of the Roman Empire


Thus it appears that the beginning of the Christian movement saw a veritable avalanche of conversions.  Possibly many of these are the direct result of the missionary activities of Paul.  But there may have been other missionaries like him who were also successful.   And so let’s simply pick a sensible rate of growth, and say that for the first forty years, up to the time when Paul wrote his last surviving letter, the church grew at a rate of 300%.   If the religion started with twenty people in 30 CE, that would mean there were some 1280 by the year 60.   That’s not at all implausible as a guess.   But growth cannot continue at that rate.  If it did, a century later, in the year 160, there would be well over a trillion Christians in the world.

So let’s say that there was a burst of initial radical enthusiasm generated by the new faith, both among people who had heard Jesus preach during his public ministry and who believed the witnesses who said that he had been raised from the dead and among those evangelized through the extraordinary missionary work of Paul and possibly others like him.  After Paul’s death there was almost certainly a rapid decline.  The change would not be immediate or steady, but we are dealing with ballpark figures here.  Say it went down on average to 60% per decade for the next forty years, while there was still a lot of energy and enthusiasm among those who thought not only that Jesus saved them from their sins but that he was coming back very soon, creating a kind of urgency for their message.   This would be a rate of growth just under 5% per year.  Every year each group of twenty people need to make just one convert.   At a rate like that there would then be something like 8381 Christians in the world in the year 100 CE.  That sounds about right.

There is no point – and no way – to do a breakdown decade after decade.  Clearly…

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Did Moses Write the Pentateuch? The JEDP Hypothesis.
Back to the Question of How Many People Converted



  1. Avatar
    marcrm68  June 24, 2016

    After Theodosis the number of Christians quickly grew to 100% of the empire, right? Rohttps://www.google.com/search?q=sol+invictus+mosaic+of+jesus&biw=1521&bih=685&source=lnms&tbm=isch&sa=X&ved=0ahUKEwi2pqz818HNAhXM2B4KHQJvBU0Q_AUIBigB#imgrc=-ovIQVIfJ0BGlM%3Aman
    Here’s an image of Sol Invictus as Jesus from the cellars of the Vatican.

  2. Avatar
    dragonfly  June 24, 2016

    Any guess on numbers at Paul’s conversion? 100? 200?

    • Bart
      Bart  June 26, 2016

      Yeah, I really don’t know, or know how we can know!

      • Avatar
        dragonfly  June 27, 2016

        I’ve been looking at your figures and I think they might be a bit misleading. Let’s assume there were 20 Christians in 30CE, and Paul converted in 33. And the average was 300% per decadefor the first 40 years = about 14.8% per year. If this was linear (which of course it wasn’t), there would have been about 30 Christians in 33 and 80 in 40. I find these figures implausibly low. Paul was so wound up about less than 30 people in the Roman empire? And after 7 years of his missionary activities there were only 80? If you tweak the first few years everything changes. If there were 100 Christians at Paul’s conversion, that’s about 70% per year, which is a large percentage, but only a few men and their families each year. But then to keep the average at 300% per decade for the first 40 years, you only need about 11-12% per year after his conversion, which is about 180% per decade. That would mean every year, 10 people would only need to convert 11-12 others between them. So those first few years make a big difference to the rates in the following years.

        • Bart
          Bart  June 27, 2016

          Yes, that’s more or less why I was saying we could tweak the numbers for ever. I just don’t think we know enough to say that Xty grew at X% for the first year, then Y% the next, and then Z% the third, etc. — though obviously it is fun to try to do so! You’re right — the earlier, the higher percentage though, almost certainly

          • Avatar
            dragonfly  June 29, 2016

            I think what I can get from this is that probably, although there would have been ups and downs, the overall trend is each year the number of conversions increased, while the percentage rate decreased. Which is not necessarily intuitive at first.

    • Pattycake1974
      Pattycake1974  June 26, 2016

      Paul mentioned 500 seeing Jesus alive, but that doesn’t necessarily mean they converted. I think Paul’s conversion had an instant wow factor and caused dozens to convert quickly. That’s not scholarly though, just my opinion.

  3. Avatar
    prairieian  June 24, 2016

    Very minor point…when you list the numbers in your book, I would do some rounding to indicate the fact you have little to no precision. Your 60 AD figure becomes 1300 or 1200. Your 100 AD figure become 8000 or 8400. Your 150 AD figure becomes 35000, etc.

    I think as well some sort of estimate as to geographical dispersion would be interesting to provide, if it is possible. I imagine some cities or areas had fairly substantial numbers, and hence notice (e.g. Pliny’s enquiry of Trajan as to what was he supposed to do with this “his” Christian population), whereas other areas might have had very marginal populations that were virtually invisible.

    The issue of nominal Christian is also interesting. That is, when good old Dad says “…we’re now all Christians…” I can well imagine the rolling of eyes from the teenage daughter and the dutiful nod of the loyal wife. Yes, the household might all be counted, but a goodly percentage of such conversions would be no more than notional at best. It all depends on definition. (The same issue applies today in that much of the contemporary Christian world is no more than culturally connected with no meaningful belief or commitment.)

  4. Pattycake1974
    Pattycake1974  June 24, 2016

    I like the list you have there. It’s much easier to digest than reading it in paragraph form.

    Even though other religions have grown at similar paces, didn’t they all come *after* Christianity? Aren’t those religions all tied to Jesus in some way? I don’t know of any other religion that grew so steadily for such a long period and endured. If so, then that would be important to know, but only if the religion or movement wasn’t affiliated with Jesus. The significance is him; he’s the phenomenon.

    • Bart
      Bart  June 26, 2016

      I’m not sure what you mean. There were thousands of religions around before Christianity, and many of them were widespread.

      • Pattycake1974
        Pattycake1974  June 27, 2016

        From the May post, it came across to me that you viewed the growth rate of Christianity as nothing really that significant or any sort of phenomenon. You mentioned the Mormon religion as having a similar pattern of growth. This post comes across to me the same way, but then after reading talmoore’s comment, he got a completely different take on your perspective. You replied that the Church’s growth was definitely remarkable. I was trying to say the same thing–maybe it wasn’t a miracle, but it certainly was remarkable.

        So now I’m wondering how you’re presenting the information in your book. If you hadn’t specifically said that you thought it was remarkable, I would have thought you felt it was very ordinary. Before, you seemed very adamant that converting people and arriving at such huge numbers in Christian population was not unique or special or even remarkable in any way. I hope I’m making sense here.

        • Bart
          Bart  June 27, 2016

          It’s remarkable because there was nothing like it before. It is not remarkable only in the sense that it’s completely feasible.

    • Avatar
      BrianUlrich  June 26, 2016

      Sikhism would be the clearest counter-example here.

    • Avatar
      J--B  June 26, 2016

      Although Muslims regard Jesus as a prophet, I doubt you could say that Islam is affiliated with or tied to Jesus in the sense that the different forms of Christianity are. It certainly does not consider him God or the Son of God.

  5. Avatar
    Servelan  June 25, 2016

    Bad tags again…whole post shows.

  6. talmoore
    talmoore  June 25, 2016

    Dr. Ehrman, I’m curious why you (and Rodney Stark) are so hung up on the numbers. As someone who regularly studies the spread of ideas (so-called memes) throughout a population as part of my research, I know that it’s well within the realm of possibility that a movement that starts with only 20 people could take over an entire empire of 30 million people within only one decade — let along thirty decades. Ten years may seem to us like a very short amount of time from the historical perspective, but we have to remember how much can happen within only ten years (within the span of only ten years Germany went from “peace in our time” to a massive Nazi empire that stretched from France to Stalingrad and finally ended up split into two countries occupied by separate superpowers; so, yeah, a LOT can happen in only ten years).

    If you don’t believe me consider the historical example of the spread of Protestantism in the 16th century. When Luther nailed up his 95 Theses in 1517, 99.99% of all Christians in Europe were (nominally) Catholic. But before even the close of the century, almost one-third of Europe’s population of almost 100 million (or ca. 30 million) had “converted” to some form of non-Catholic Christianity. That’s some rapid growth right there (though, to be fair, the rapid spread of Protestantism was heavily aided by the invention of the printing press).

    But the math also allows for such rapid growth. Let’s say Luther simply converted one person a day to Protestantism over the course of ten years, and each person he converted likewise converted a person each day for ten years, and that person converted a person each day for ten years, and so on and so forth. How many people would be converted to Protestantism within in the decade? Well, the math is rather easy. The population of Protestants is going to double every day, so we just raise 2 to a power equal to the number of days in ten years, i.e. 3650. But even with the necessary division by 2 in order to make up for the growth being spread out over 20 years that would still leave us with 2 raised to the power of 1865. Now, 2 raised to the power of 1865 is such a mindbogglingly large number that our sun would be long dead and the earth long gone before we could even finish writing out that number. (Just to give you an idea, know that 2 raised to the power of 50 is around 11 quadrillion.) And that’s with a logistically reasonable one conversion per day. That’s the power of exponential growth. So…I guess my point is I’m not quite sure why you (or Rodney Stark) are so fixated on affirming a reasonable rate of growth when, as I hope I’ve made relatively clear, Christianity’s rate of growth is so within the realm of possibility as to seem uninteresting. (And you can quote me on that.)

    • Bart
      Bart  June 26, 2016

      I’m not really interested in claiming that it was miraculous growth. I’m simply trying to figure out how fast it did grow, in terms of both numbers and rates. It certainly could have grown much faster or slower. But however you crunch the numbers, it’s remarkable that it went from being about 20 lower class peasants around the year 30 to around 30 million devotees around the year 400.

    • Pattycake1974
      Pattycake1974  June 26, 2016

      It’s interesting that you think he and Stark are insinuating a miracle took place with the growth rate because I got the exact the exact opposite from his posts.

      • talmoore
        talmoore  June 27, 2016

        It’s not that I think Ehrman and Stark are insinuating a miraculous growth, but that they are arguing against a miraculous growth as if the growth could be perceived as miraculous. I’ve known plenty of hardcore Christians who do believe the growth of Christianity was somehow miraculous, so I can appreciate the need to lay out the numbers before them, but, in this case, I think it’s enough to merely point out that Christianity’s growth was anything but exceptional. Indeed, in comparison to some movements (e.g. Islam) Christianity’s growth was almost glacial.

  7. Avatar
    RonaldTaska  June 25, 2016

    Wow! These numbers are, indeed, at first glance, “striking” and “staggering,” but at the same time, as you explain, not “implausible” if driven by “family conversions” making them similar to the rate of growth of Mormonism by “family conversions.”.

    I was especially intrigued by what for me was the totally unexpected decreased “rate” of growth after Constantine since there then existed fewer non-Christians to convert. Thanks

  8. Avatar
    Adam0685  June 25, 2016

    Please write a textbook on the history of earliest Christianity! There is a market! Most are boring and dull even for people who are interested in the topic! Or they’re heavily biased by an evangelical/conservative lens (and many that aren’t are outdated).

  9. Avatar
    Wilusa  June 25, 2016

    An OT question that just occurred to me: Did the Romans, at some point in the Christianization of the Empire, stop using crucifixion as a method of execution? If so, was there an Empire-wide ban at some point, or did the custom die out at different times in different regions?

    When I thought about this, I remembered that as a child, I’d believed not only that crucifixion was the most painful conceivable type of death, but that Jesus was the only person who’d ever been subjected to it! I don’t think anyone ever told me that; I’d just assumed it. But I *wouldn’t* have assumed it if I’d had competent teachers.

    • Bart
      Bart  June 26, 2016

      Yes, eventually Constantine forbade crucifixion (though I’m not sure completely)

  10. SBrudney091941
    SBrudney091941  June 25, 2016

    As I read this, I’m reflecting, as a (cultural) Jew, on Jewish population growth or, rather, its absence. What a state of affairs: Jews whose numbers around Jesus’ time might have already been 2-5 million never had, after that time (I guess it’s accurate to say), a growth rate anything like Christians did. Somewhat ironic that they started out (in that period, I mean) with so many and ended with so few while those who incorporated some of Judaism, who began with so few, yet became so many. I guess the main reason is that you don’t go into full revolt against Roman rule and expect to flourish under Roman rule after that. And then, of course, Constantine. Then again, not all of Jewry revolted against Rome. Most Jews lived outside Palestine. Any thoughts?

    • Bart
      Bart  June 26, 2016

      I don’t think it wsa the revolts that did it. The numbers probably dropped through the massive pogroms of later times.

      • talmoore
        talmoore  June 26, 2016

        Josephus claims that millions of Jews were killed in the war from 66 to 73, with a million dying in the siege of Jerusalem alone. Dr. Ehrman, do you think Josephus is exaggerating? And if so, what would be your educated guess as to the body count?

        • Bart
          Bart  June 27, 2016

          Yes, definitely an exaggeration. Josephus can be shown to exaggerate numbers because he often refers to the same event in Wars and in Antiquities, and gives different numbers. I don’t have any opinion about the actual numbers for the fall of Jerusalem, but would love to know of some if you run across any.

  11. Avatar
    RonaldTaska  June 26, 2016

    I recently had a long and good conversation with a Catholic. He contended that it is very important to be “fruitful and multiply” as the Bible commands in order to eventually outnumber the Muslims. I guess another way to look at this is that religious groups have figured out the powerful effect of “family conversions” on increasing numbers. If a woman marries and converts her husband and then they have 2 children who convert that quickly results in quadruple the number in a decade and if many do this then eventually you get “huge” numbers. .

    • Pattycake1974
      Pattycake1974  June 26, 2016

      That definitely sounds like an interesting conversation.

    • Avatar
      Wilusa  June 26, 2016

      Wow. Having been raised Catholic, I’m horrified! In my experience, Catholics never even read the Bible, let alone thought about outnumbering Muslims.

      A few years ago, a Catholic friend of mine – the kind who goes to Mass every day – actually asked me whether these “Muslims” were the people who were called “Mohammedans” when we were growing up!

  12. Avatar
    frfouger  June 27, 2016

    When estimating the conversion rate, do you take in account some of the data provided in Acts (4:4)?

  13. Avatar
    Eric  June 27, 2016

    I have a hard time reconciling a movement of 100 or so (so how many in Antioch? 20?) somehow inciting enough ire in Paul to become his life’s work/hobby (persecuting them).

    Paul’s own story (leave Acts out of it) feels like there were a lot more around during his persecuting days (because he would have only been in contact with a fraction of the total number, geographically).

  14. Avatar
    clifh  June 29, 2016

    Somewhere you need to note that we’re talking about net growth. If we assume the death rate equals the birth rate and that all births within the Christian community become Christian, then indeed the net growth is that same as the rate of new conversions.

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