There’s a project I’m working on where it is very easy to get lost in the weeds. For example: I’d like to be able to say: the typical feudal baron holds between x manors.
Not being an historian, but being pretty good at finding answers, I’ve found the details of feudalism to be very difficult to nail down. This is partly because “feudalism” is a nebulous term and conditions were different in various places and times within the Middle Ages, and partly because records are vague, incomplete, and often absent. Being fluent only in English, I realized from the outset that I should focus on England just to have easier access to scholarship and reference works, but from what I can tell population and property are only really well-documented by the Domesday Book (after the Norman conquest, in 1086) and a poll-tax lists from 1377-1381. Obviously this leaves a big gap in enumeration because 12th-13th century were absolute boom years in terms of population, due to advances in agriculture and trade, and the 14th century saw a precipitous collapse due to pestilences of crops, murrains of livestock, and of course the Black Death, not to mention the probable beginnings of the “Little Ice Age.” Moreover these sources don’t count paupers — beggars in both cases and mendicant friars in the case the poll taxes– nor women & children under 16 or so. So the total population can only be estimated. But it turns out the exact number of manors is also unknown.
What I have seen repeatedly is an estimate that medieval England had 5000-6000 knight’s fees: units of land considered sufficient to support a knight and his retinue, and generally each manor would be a knight’s fee. That should make it pretty simple. Estimate 5500.
But: each manor would have its own church, representing a parish. But I’m usually finding estimates of 10,000 to 13,000 parishes in Medieval England. This is almost certainly based on the number of modern Anglican parishes, which have the number variously reported as 13,000 and 10,480. A vital piece of missing information I found was that about 1/3 of the modern parishes in England were created after after the middle ages, so depending on which number we trust, there would have been 8,666 (13,000 x 2/3) or 6987 (10,480 x 2/3) parishes in Medieval England. I’m going to guess that 13,000 is the total Anglican parishes including Wales, Ireland, and Scotland, and 10,480 is just England. This is admittedly a guess, since I haven’t seen any specific sources on how those numbers were generated.
The second number fits a lot better with the number of knight’s fee’s. Let’s call it 7000. Supposing about 10% of the population lived in cities, we could pretty readily justify 1/10 of the parishes being urban: that is parishes not on manors but in parts of cities. This gets me to roughly:
about 5,500 parishes on manors
about 700 parishes in cities (including parishes centered on cathedrals rather than smaller churches)
about 1300 parishes still unaccounted for
But there were also at least 600 monastic communities and 150 friaries in early 13th century England. Each of these has a chapel or church, possibly representing a parish (all those lay brother serfs need somewhere to pray too!). So now we’re down to 550 “extra parishes.”
This is a difference I can tolerate. Maybe I should have used the largest guess, 6000 knight’s fees, so another 500 parishes are accounted for. Or maybe some 10% of the 5500 manors are large enough to have two churches and thus two parishes. (Or: the “service chapels” that existed on larger manors to serve the more isolated peasants at their extremities should count as second parishes?) These two-parish manors are presumably bigger than a knight’s fee. That’s fine. We know some estates were on lands considerably smaller — one in Oxford, I read, was just 5 acres, which really wouldn’t support any serfs.
BUT, you say, weren’t those abbeys and friaries built on land that used to be enfoeffed or granted to the Church out of those 5000-6000 knight’s fees we counted earlier? Well, I think so. But I looked a little more for the source of the 5000-6000 estimate, and seems to stem from the Domesday Book, which remember was an assessment of England in 1086. England was gradually clearing forests and otherwise reclaiming “waste” land for agriculture, so I think entirely plausible that new estates were created from cleared land and given to knights/barons/earls or the Church.
All this just leads back to saying: Medieval England can plausibly be said to have had around 5500 secular (not Church-held) manors. The Church held an estimated 1/4 to 1/3 of the land, and held many manors. But the Church was likely to send money (scutage) rather than armed men in times of war. I’ll assume that the crown would not want to reduce it’s military potential and maintained the same approximately 5500 knights fees in the hands of knights and barons. Any additional arable land is consumed by freeholders, the Church, and the royal demesne (manors held by the crown), and won’t be held by any baron.
It looks like there were around 2000 barons in Medieval England. So the average baron held 5500/200 = 27.5 knight’s fees. This actually looks like a reasonable number. Some will have much fewer, and some more.
So, there’s my best guess, having scanned a few books and articles. And Googled a lot more than I’d like to admit. And thrown around numbers in an effort to convince myself. I’ll leave to an actual historian or economist to figure out the correct numbers, but this should be verisimiltudinous enough for my purposes.
*You know damn well there’s more than two.
Swords & Dorkery 
Well I could have saved myself some some time by asking ChatGPT:
“Estimating the exact amount of arable land in 13th century England is challenging, as there is no comprehensive record of land use from that period. However, it is estimated that around 25% of England’s total land area was arable in the 13th century.
Regarding the amount of land each baron held, it varied greatly depending on their social status, wealth, and position in society. The term “baron” was used to refer to a range of people from the king’s closest advisors to minor landowners with only a few acres of land.
However, as a rough estimate, it’s believed that the average baron in the 13th century held around 20,000 acres of land. This amount of land would have included both arable and non-arable land, such as forests, pastures, and meadows. Some of the wealthiest barons could hold much more land, sometimes tens of thousands of acres, while smaller landowners might have only a few hundred acres.”
20,000 acres is perhaps 20 knight’s fees, which is with the ballpark of what I guesstimated above.