- Kingdoms in the real world varied greatly in size.
- The sizes you get by following the guides in the DMG are perfectly reasonable
- You can (and probably for reasons of interest) vary them a lot
- The suggestion in the DMG that their scale corresponds to the size of Britain is nonsense.
A single sheet of hexagonal paper with 5 hexes per inch is ideal for most cards.
- Letterhead is 11 "tall.
- As a result, the letterhead has a height of 55 hexes
(Province scale) each hex represents 1 mile
- The letterhead is 55 miles across the province
(Provincial scale) an area that can be traveled in one day in any direction from the center of the map
This assumes, therefore, that a party can cover 27.5 miles a day.
the normal movement speed is 3 miles per hour (source)
This maps to real world values:
most hikers will average about 2 to 3 km at the hour. (source)
This implies that a little less than 10 hours a day will be spent walking. Given the food breaks and setting up the camp, this is feasible given a day spent traveling.
On a map at the scale of the realm, each hex represents 6 miles
So we can just multiply everything by 6
- Letterhead is 396 hex / miles high
- 396 miles / 27.5 miles per day = 14.4 days
A map on the scale (of the Kingdom) covers a large region, the size of Great Britain.
From now on, D & D connects it directly to the real world. Britain is about 700 miles long and about half that wide.
The calculation is wrong here.
That said: a kingdom of 395 km by 306 is perfectly reasonable:
So, you write your story or build your campaign world. How many villages does this give us in a kingdom? Choose the size of your kingdom and choose the above. A kingdom could be huge, but some were little more than a region the size of a small county. The determining factor is not size, but independence – a king does not owe feudal allegiance to a higher secular authority. (source).
… that's just not the size of Britain.
Since this source mentions "the size of a small county".
The largest length (from Runtland) from north to south is only 29 km and its greatest width from east to west is 27 km. (source).
It's significantly smaller than 396 × 306!
And you can go bigger if you wish, it is (presumably) the world of your campaign that you map and whose kingdoms of uniform size would look rather strange!
And as fun to share:
Land's End to John where Groats is crossing the entire length of the island of Britain between two ends, southwest and northeast. The traditional distance by road is 1,407 km and takes most cyclists between 10 and 14 days; the course record is nine days. Off-road walkers typically walk about 1,900 miles (1,200 miles) and take two or three months for shipping. (source)