# [top]The Basics

##### [top]The Core Mechanic

Whenever you attempt an action that has some chance of failure, you roll a twenty-sided die (d20). To determine if your character succeeds at a task you do this:
• Roll a d20.
• Compare the result to a target number.

If the result equals or exceeds the target number, your character succeeds. If the result is lower than the target number, you fail.

### [top]Dice

Dice rolls are described with expressions such as 3d4+3, which means roll three four-sided dice and add 3 (resulting in a number between 6 and 15). The first number tells you how many dice to roll (adding the results together). The number immediately after the d tells you the type of die to use. Any number after that indicates a quantity that is added or subtracted from the result.

##### [top]d%

Percentile dice work a little differently. You generate a number between 1 and 100 by rolling two different ten-sided dice. One (designated before you roll) is the tens digit. The other is the ones digit. Two 0s represent 100.

### [top]Rounding Fractions

In general, if you wind up with a fraction, round down, even if the fraction is one-half or larger.

Exception: Certain rolls, such as damage and hit points, have a minimum of 1.

### [top]Multiplying

Sometimes a rule makes you multiply a number or a die roll. As long as youre applying a single multiplier, multiply the number normally. When two or more multipliers apply to any abstract value (such as a modifier or a die roll), however, combine them into a single multiple, with each extra multiple adding 1 less than its value to the first multiple. Thus, a double (×2) and a double (×2) applied to the same number results in a triple (×3, because 2 + 1 = 3).

When applying multipliers to real-world values (such as weight or distance), normal rules of math apply instead. A creature whose size doubles (thus multiplying its weight by 8) and then is turned to stone (which would multiply its weight by a factor of roughly 3) now weighs about 24 times normal, not 10 times normal. Similarly, a blinded creature attempting to negotiate difficult terrain would count each square as 4 squares (doubling the cost twice, for a total multiplier of ×4), rather than as 3 squares (adding 100% twice).

Back to System Reference Document. This article is a D20 reference page The System Reference Document is a comprehensive toolbox consisting of rules, races, classes, feats, skills, various systems, spells, magic items, and monsters compatible with the d20 System version of Dungeons & Dragons and various other roleplaying games from Wizards of the Coast. Contributors: BRadmin , Arjan Created by Arjan , 11-03-2011 at 07:42 PM Last edited by BRadmin , 11-03-2011 at 11:51 PM 0 Comments, 4,616 Views

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