Dice Numbering Conventions
Having gamed since D&D first addition when I started in the early 80s, I'm writing on this from more than 25 years of table-top gaming experience through a -wide- variety of systems. Of course many dice production companies no longer follow dice numbering standards for whatever reason (usually it's just unknowing ignorance) - so as it was previously mentioned, the standards are (currently) seldom followed. That said, these are the standards.
While there is variation in numbering systems, there is a correct format.
The highest number on the die plus the lowest number should always be the value of the numbers on opposite sides of the die. (I will note that d10/percentile has two correct builds). The exception is the build of a d4.
Standard dice formats:
d4 = **SEE NOTE 1**
d6 = 7 (6/1, 5/2, 4/3)
d8 = 9 (8/1, 7/2, 6/3, 5/4)
d10/Percentile **SEE NOTE 2**
d12 = 13 (12/1, 11/2, 10/3, 9/4, 8/5, 7/6)
d20 = 21 (20/1, 19/2, 18/3, 17/4, 16/5, 15/6, 14/7, 13/8, 12/9, 11/10)
This format is followed for all greater number dice (d30, d100, or rarer combinations).
**NOTE 1**
d4 has two builds, one where the result number is on the base, and one where the result number is on the top point. d4 is also the easiest NOT to make incorrectly, as if it IS incorrect, it can't be made (ie: you'd not have a decisive roll result, it would be something like 4/3/3, or 2/1/3, etc)
d4 "base build" = whatever the base number is -must- be excluded from the one invisible side. This means that if the base number is 4, then the unseen side (touching the table) must have 1/2/3. Additionally, the result number must align with the closest edge of the invisible face on ALL visible sides.
Result = 1
Invisible Face = 2/3/4
Result = 2
Invisible Face = 1/3/4
Result = 3
Invisible Face = 1/2/4
Result = 4
Invisible Face = 1/2/3
d4 "point build" = where the result roll is on the top point, the bottom corners of the visible sides must all have matching/corresponding numbers, and the invisible side must exclude the result number entirely, and the numbers must align with the base point (non-result) numbers.
So, if the top point shows a 4, then the three visible points must show 1, 2, and 3, respectively while the invisible points must contain only 1, 2, and 3, and each number must align with the related visible point (non-result) number.
**NOTE 2**
If using a combination of d10 and d10 percentile to generate a 0 to 100 roll, then strict opposite numbering composition must be used.
d10 with 0 treated as 10 MUST combine with percentile d10 with 00 treated as 00. (d10 build 1 matches with percentile build 2)
d10 with 0 treated as 0 MUST combine with percentile d10 with 00 treated as 100. (d10 build 2 matches with percentile build 1)
**BUILD 1** (0 treated as 10)
d10 = 11 (0/1, 9/2, 8/3, 7/4, 6/5)
**BUILD 2** (0 treated as 0)
d10 = 9 (9/0, 8/1, 7/2, 6/3, 5/4)
**PERCENTILE BUILD 1** (00 treated as 100)
Percentile d10 = 110 (00/10, 90/20, 80/30, 70/40, 60/50)
**PERCENTILE BUILD 2** (00 treated as 00)
Percentile d10 = 90 (90/00, 80/10, 70/20, 60/30, 50/40)
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Hope this wasn't too confusing, and I hope this helps.