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My character leveled up and I rolled a D10 to determine the rise in hitpoints. The dice that I used goes from 0 to 9 and I rolled a zero. The DM told me that this means I only add my modifier (0 + 3 = 3).

I didn't agree with this and think it counts as 10. The 0 is probably there for cosmetic reasons.

Who is right in this situation?

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    \$\begingroup\$ related Why does a d10 count from 0 to 9? \$\endgroup\$ – enkryptor Sep 2 '18 at 14:05
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    \$\begingroup\$ Does your DM always treat 10 as "0" for d10 (for damage, etc)? Or was it only about hit points? \$\endgroup\$ – enkryptor Sep 2 '18 at 14:27
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A zero on a d10 counts as 10.

This isn't clearly specified in the 5th edition rules, but is clearer in earlier editions of the game, and widely understood among long-time RPG players. However, we can still surmise from the D&D 5th edition rules that d10 is 1-10 like all other dice, from the following:

  • Hit Dice by Size (Monster Manual p.7) confirms that the average of 1d10 is 5½, which is consistent with a range of 1-10. (The average of 0-9 would be 4½.)
  • The fighter receives 10 hit points at 1st level. This wouldn't make sense if a d10 couldn't actually reach 10. All other classes receive the highest value of their roll at 1st level (e.g. the monk receives 1d8 per level, and 8 at first level).
  • The fighter may take 6 hit points instead of rolling 1d10. This is consistent with the average result of 1-10 (5.5) rounded up. All other classes work the same way (e.g. the monk can take 5 hit points, equivalent to the average of 1-8 (4.5) rounded up). But the average of 0-9 is 4.5, so if 1d10 really meant 0-9, we would not expect to see the fighter allowed to take 6.
  • The D&D Beyond character builder can confirm that if you create a fighter above level 1 with rolled hit points, they can indeed gain a roll of 10 on their hit points.

The reason for the zero is that in many games including D&D, two d10s can be rolled together to generate a two-digit percentile number between 00 and 99. As per PHB p.6, "Two 0s represent 100," another precedent which suggests that zero on the dice doesn't necessarily mean zero.

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    \$\begingroup\$ Nice proof you've collected here, but imho you should also point out the Defining Event table of the Folk Hero background (PHB, p. 131): It lists all the possible outcomes of the d10 from 1 to 10. \$\endgroup\$ – fabian Sep 4 '18 at 8:49
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    \$\begingroup\$ It will always bug me that it's 00-99 instead of 01-100. Considering the 0 on a d10 being 10 by itself you would think rolling 00 would be 1-10, 10 would be 11-20... 90 would be 91-100. But nooooo, it magically turns into a 0. \$\endgroup\$ – James Sep 5 '18 at 15:54
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You are correct. Many old school d10s are marked 0-9 but you count the 0 as 10.

If he doesn’t listen to reason, next level use one of the d10s marked 00-90 instead and demand your 45 or so hit points from that roll.

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    \$\begingroup\$ Let's make D6 and D10 dices with 99.'s on all sides. \$\endgroup\$ – Cœur Sep 9 '18 at 11:02
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The Player's Handbook discusses dice on p. 6, in the subsection titled "Game Dice":

In these rules, the different dice are referred to by the letter d followed by the number of sides: d4, d6, d8, d10, d12, and d20. For instance, a d6 is a six-sided die (the typical cube that many games use).

Percentile dice, or d100, work a little differently. You generate a number between 1 and 100 by rolling two different ten-sided dice numbered from 0 to 9. One die (designated before you roll) gives the tens digit, and the other gives the ones digit. If you roll a 7 and a 1, for example, the number rolled is 71. Two 0s represent 100. Some ten-sided dice are numbered in tens (00, 10, 20, and so on), making it easier to distinguish the tens digit from the ones digit. In this case, a roll of 70 and 1 is 71, and 00 and 0 is 100.

It does not actually say that a d10 generates a number between 1 and 10, but that is how it is interpreted. The zero means 10.

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  • \$\begingroup\$ The 0 does mean ten on a d10, but percentile dice aren't a good way of showing it. If you roll e.g. 40 and 0, that 0 is zero. \$\endgroup\$ – Ray Sep 6 '18 at 1:30
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A 0 counts as a 10

The Player's Handbook talks about dice referring to each dX as a die with X sides implying that the number of sides is the maximum roll through context.

There is also some circumstantial evidence in the spell confusion, which states:

An affected target ... must roll a d10 at the start of each of its turns to determine its behavior for that turn.

\begin{array} {|c|l|} \hline 1 & \text{The creature uses all its movement to move in a random direction...} \\ \hline 2-6 & \text{The creature doesn't move or take actions...} \\ \hline 3-7 & \text{The creature uses its action to make a melee attack ... randomly} \\ \hline 9-10 & \text{The creature can act and move normally.} \\ \hline \end{array}

Since there is no 0 in the table but a 10 is included, the most reasonable assumption is that a 0 is a 10.

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A d6 goes from 1 to 6. A d12 goes from 1 to 12. A d10 goes from 1 to 10. That zero is the ten.

And in case your GM starts wondering...

Why is it a zero then?

While rarer in modern DnD, it's quite a common use of d10 to roll two at the same time to simulate a roll of d100. This is why these dice are often sold in sets with one die having "tens": 00, 10, 20 and so on, and the other having just "ones": 0, 1, 2, 3 and so on. One'd roll two dice and combine the tens and ones to get a result, eg. 80 and 7 yield an 87, with the special case of 00 and 0 typically but not universally meaning 100. Using d10's as d100 is the use where zero means a zero (except in the 00+0 case).

Even when intended for percentage rolls, the "ones" die could of course include a ten instead of a zero, at risk of being suspectible to be confused with the "tens" die (both'd have a 10), being somewhat uglier (at least to my taste) and causing a fair amount of "sixty, uh, tens" which might be jarring to those of us who aren't French. Indeed, d10s with numbers 1-10 do exist, they just don't seem to be as common.

When used as a single die, the aforementioned purpose of the 0 doesn't really exist, so a roll 0 on a d10 is a ten.

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    \$\begingroup\$ Ah, how I love to work in a number-intensive role and knowing just enough french that people expect me to follow along as they read up 5 or 6-digit numbers. I hear somewhere between 8 and 19 digits. Quattre-vingt-seize - did you mean 96 and more numbers will follow or was that 802016? You guys... ;-) \$\endgroup\$ – Stian Yttervik Sep 4 '18 at 7:26
  • \$\begingroup\$ @zakinster Nay, 00+1 for instance is 1, not 101. \$\endgroup\$ – kviiri Sep 5 '18 at 10:12
  • \$\begingroup\$ @kviiri ah yes, didn't think this through, I'll delete my confusing comment. \$\endgroup\$ – zakinster Sep 5 '18 at 11:32
  • \$\begingroup\$ Also may be worth mentioning, all dice used single digits in the very early days of D&D. D20s were marked 0-9 twice, with one set inked in a different color. I assume there's some reason tied to how the dice were manufactured. \$\endgroup\$ – Random832 Sep 5 '18 at 17:22

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