A d100, also called a percentile die, is a 100-faced die in which every value from 1 to 100 has exactly a 1 in 100 chance of landing. Each face is equally likely, the expected average of a single roll is 50.5, and the die is the workhorse of percentile tables and percentage-based tabletop role-playing games. Physically, a true d100 is a rare 100-sided polyhedron (a pentagonal trapezohedron) that most players substitute for two standard d10s — one die is read as the tens digit (00, 10, 20, …, 90) and the other as the units digit (0–9), giving the same 1–100 range. A digital d100 dice roller skips both physical shapes and draws a single uniform integer from 1 to 100, which is the simplest way to get a fair percentile result in your browser. The Dice Roller exposes this through its Custom sides control, so you can type 100 and roll percentile results without owning any physical dice.
What a d100 actually is in role-playing games
The d100 is older than most dice sets you will find on a game store shelf. It appeared in wargaming and role-playing supplements in the 1970s as a way to express probability in plain percentages rather than in d20 odds, and it was folded into games like Traveller, Call of Cthulhu, and later Warhammer Fantasy Roleplay as the default resolution mechanic. In Dungeons & Dragons the d100 is rarely the main roll, but it shows up in the Dungeon Master's Guide random tables (encounter, treasure, dungeon dressing), the Wild Magic Surge table for sorcerers, and a long list of optional subsystems from Boons to Madness. In every case the rule is the same: roll a d100, read the result, find that row on the table. No modifiers, no proficiency, no damage bonus — just a clean uniform draw.
Common uses for a d100 dice roller
Percentile dice are the workhorse of several tabletop role-playing systems and a handful of common random-table tasks.
- D&D wild magic and random tables. The Wild Magic Surge table, the Draconic Polymorph table, and many Dungeon Master's Guide random encounters call for a d100 roll to pick a specific row out of 100.
- Call of Cthulhu and horror RPGs. Call of Cthulhu's skill checks resolve against a percentile chance equal to your skill value, and Sanity losses often pull from d100 tables in the Keeper's handbook.
- Warhammer Fantasy Roleplay and percentage systems. WFRP, Dark Heresy, and the World of Darkness lines resolve nearly every action as a percentage roll under your stat.
- Settlement, weather, and loot tables. Hex crawls, dungeon generators, and weather rules frequently map 1–100 outcomes to long tables of flavor text.
- Plain percentage decisions. When you just need a fair 1 to 100 number — to split a bill, pick a film out of a long shortlist, or sample a survey response — a d100 is the cleanest source.
Roll a d100 in your browser
The following steps walk through rolling a percentile die with the Dice Roller. The tool runs entirely client-side, so once the page is loaded the rolls are instantaneous and nothing is uploaded.
- Open the Dice Roller and tap Custom in the dice-type row.
- Type 100 into the sides field so the tool knows to treat the next roll as a percentile die. The Custom field accepts any number from 2 to 1000.
- Use the − and + stepper to set how many d100s you want to roll at once — the tool accepts up to 12 dice in a single click. Leave it at 1 for a single percentile result, or bump it up to several when a table asks for a sample.
- Press the Roll button.
- Read each individual result, the combined total, the entry appended to your recent roll history, and the updated session stats (count, average, min, max).
Because everything happens in the browser, the same flow works on a phone, tablet, or laptop, and the roll history stays visible on the same screen so you can spot-check a long table without losing your place.
Why a digital d100 needs a fair source of randomness
Most quick "roll a d100" widgets use JavaScript's Math.random(), which is fast but is not formally guaranteed to be unbiased across engines. For a percentile die this matters more than for a d20, because a d100 has 100 faces: a small bias toward high or low numbers becomes obvious after a few dozen rolls. The Dice Roller avoids this by using crypto.getRandomValues(), the browser's cryptographically secure pseudo-random number generator (CSPRNG), to draw each face. A CSPRNG is designed to be statistically uniform, so each of the 100 possible results lands roughly 1 percent of the time. Internal testing rolled a d6 sixty thousand times and confirmed the distribution passes a chi-square fairness check; the same uniformity principle applies to a d100, since each face is just a wider bucket of the same underlying random source. Because percentile rolls are often used for skill checks and percentage decisions, that uniformity is exactly what makes the result trustworthy.
d100 vs two d10s: how percentile reading works
Different sources of percentile numbers handle the tens and units differently, which changes how doubles like 33 or 77 are read. The table below summarizes the three common approaches.
| Approach | How the 1–100 number is produced | Result of a "double" (e.g. 30 + 30) |
|---|---|---|
| Single physical d100 | One 100-faced roll. | Reads as exactly that face — usually 30, 70, etc. |
| Two d10s (tens + units) | One die gives tens (0, 10, 20 … 90), the other units (1–10 or 0–9). | Often treated as 100 (a "00 + 0" or "0 + 100" reading), so doubles rarely appear. |
| Digital d100 dice roller | Single uniform integer from 1 to 100. | Reads as the integer itself, so doubles are perfectly possible. |
For random-table work this difference rarely matters: a d100 table is usually designed around one convention or the other and will state it. The clean rule is that whatever the table says the result means, the digital Dice Roller will treat your roll as a flat 1–100 integer, so map 100 to whatever row the table assigns to "100" and you are set.
Quick reference: standard polyhedral dice
The d100 sits at the wide end of the polyhedral set used in tabletop RPGs. The full standard range, and where each die typically shows up, is summarized below.
| Die | Faces | Where it is most often used |
|---|---|---|
| d4 | 4 | Dagger and small weapon damage, ability score generation in some systems. |
| d6 | 6 | Board games, hit points, ability score generation (4d6 drop lowest). |
| d8 | 8 | Longsword damage and other medium weapons in D&D. |
| d10 | 10 | Fireball damage, the "units" digit when paired with another d10 for percentile. |
| d12 | 12 | Greataxe damage, barbarian hit-die rolls, larger weapon damage. |
| d20 | 20 | Attack rolls, saving throws, skill checks, advantage and disadvantage. |
| d100 | 100 | Wild Magic Surge tables, random tables, Call of Cthulhu, Warhammer-style percentage systems. |
The Dice Roller exposes the first six as dedicated buttons and d100 through the Custom sides control, so you can switch from a d20 attack roll to a percentile wild-magic check without leaving the same tool.
Using d100 rolls as a quick probability demo
A single d100 is the simplest fair-uniform distribution you can hold in one hand: each outcome has the same 1 percent chance, and the average of a single roll is (1 + 100) / 2 = 50.5. Roll 2d100 many times and add them, and the totals start to form a recognizable triangular bump centered around 101, just like 2d6 peaks at 7 because there are more ways to roll middle totals than extremes. The Dice Roller's session stats — average, min, max, count — double as a live look at that distribution, which is handy if you are teaching expected value, comparing uniform and summed dice, or just want to sanity-check your mental model of what "fair" looks like after several rolls. A few minutes of percentile rolling is usually enough to watch the running average settle toward 50.5, which is the visual confirmation that the CSPRNG is doing its job.
For a deeper look, see Dice Roller D20: Roll Fair Polyhedral Dice.