Dice and Math - How to do anything in the game
Rolling Dice - How to play D&D in 3 steps
Whenever you want to do something in this game, like climbing a tree, hitting that kobold who just stabbed your side with a spear, or simply flirting with your local barmaid, you roll a twenty-sided die (hereby referenced as d20). To determine if your character succeeds or not, you simply follow these 3 steps.
- Roll a d20.
- Add any relevant modifiers.
- Compare the result to a target number.
If the result equals or exceeds the target number, your character succeeds. Otherwise, you fail.
Fighter Bob wanted to rescue his girlfriend's cat from a tree that was tad bit too high. Bob rolled his Athletics check to beat the target number of 15. Unfortunately, he only rolled 13 and failed the check. As a result, Bob fell down from a tree he was climbing and got a nasty bump on his head instead.
Dice expression
Dice rolls are typically written as expressions such as "2d6+4," which translates to "roll two 6-sided dice and add 4" (Range of 6 and 16). The red number indicates how many dice are to be rolled. The blue number indicates what kind of dice are to be rolled (d4 = four-sided dice, d6 = six-sided dice, etc). Finally, green number is a modifier. It is a flat number that is either added or subtracted after the dice are rolled first.
d%
d% is called a Percentage dice. It can generate a number from 1 to 100 by rolling two 10-sided dice. First dice indicates the tens digit, while the second dice indicates the ones digit. Two 0s (or two 10s depending on the dice) represent 100.
Rogue Valentine rolls 1d4+3+2d6 for his dagger sneak attack damage. First he rolls a single 4-sided dice which he gets 3. And then he rolls two 6-sided dice which he gets 2 and 4 respectively. Finally, he adds all the numbers together and add the 3 to get the total of 12 damage. That equals one dead Kobold.
Rounding Fractions
If, by any chance, you run into a fraction (yes, fractions exist in this game. Although it's usually from out-of-game math such as character building), you always round down. This applies if the fraction is one-half or larger. There are some exceptions though. Things like damage rolls and hit points have a minimum value of 1.
Multipliers
Sometimes the game will make you multiply a number or a die roll (like critical hit). As long as you're applying a single multiplier, multiply the number normally. However, when multiple multipliers are introduced, they are resolved additively. That means x2 and x2 together results in x3, not x4. x2 and x3 together results in x4.
When applying multipliers to real-world values such as weight or distance, apply the multipliers like how you normally would.
Modifiers
A modifier, as mentioned above, is a flat number that is either added to or subtracted from the dice rolls. If it is being added, it is a bonus, while if it is being subtracted, it is a penalty.
Stacking
There are many type of different modifiers in this game. Modifiers can be stacked as long as they come from different sources and have different types (or no type at all, which is very rare). Modifiers do not stack if they have the same type or come from same source (such as from the same spell cast twice), unless otherwise mentioned. If the modifiers to a particular roll do not stack, only the best bonus or the worst penalty applies. There is one exception though. Dodge bonus and Circumstance bonus do stack with one another unless otherwise specified.
Modifier Types - General
Ability Modifier
This bonus (or penalty), comes from your ability score. More information about this later.
Alchemical Modifier
This comes from alchemical stuff like antitoxin.
Circumstance Modifier
This bonus usually comes at DM's discretion. It is basically what we call a situational bonus, and the source of this bonus may vary. These bonus can stack with each other as long as the sources of these bonus are different.
Competence Modifier
This bonus affects a character's performance of actions. This may come from bard's inspire competence or tools. This bonus may apply on attack rolls, saving throws, caster level checks, or any other checks that has to do with skills. This does not apply on flat ability checks, damage rolls, initiative checks, or other rolls that are not related to character's level or skill ranks.
Insight Modifier
This bonus improves performance of an action by granting the character an almost precognitive knowledge of what might happen.
Luck Modifier
This bonus represents good (or bad) fortune.
Morale Modifier
This bonus represents the character's hope, courage, and determination.
Racial Modifier
This bonus comes from character's racial traits. If a character's race changes, they lose all of their previous racial modifiers.
Resistance Modifier
This bonus affects saving throws, providing extra protection against harm.
Sacred/Profane Modifier
This bonus comes from the power of good (or evil).
Size Modifier
This bonus comes from the character's size. This bonus apply to Armor Class, attack rolls, stealth checks, grapple checks, and various other checks.
Modifier Types - Armor Class
Amor Bonus
This comes from, you guessed it, armor. The said armor can be your average armors or any spells that emulates armor (such as Mage Armor). This bonus does not apply against touch attacks, which will be explained later.
Deflection Bonus
This bonus usually comes from a spell or magic effect that makes attacks veer off harmlessly. Deflection bonus does apply against touch attacks.
Dodge Bonus
This bonus never comes from spells or magical effects. This bonus comes from physical skill at avoiding blows and other ill effects, usually comes from feats or as class features. Dodge bonus can be stacked with different source of dodge bonus, and does apply against touch attacks.
Enhancement Bonus
This bonus comes from increased sturdiness or effectiveness of armor, weapon, shield, or even ability score. Multiple enhancement bonus on the same object (like weapons and armors) or ability score do not stack. Because the bonus comes from the object, they do not apply against touch attacks.
Natural Armor Bonus
Usually the traits of the monsters, this bonus comes from naturally tough hide. This bonus may come from certain spells (such as Barkskin spell). This bonus does not apply against touch attacks.
Shield Bonus
This bonus comes from, you guessed it again, shield. The said shield can be your regular shield or any spells that creates a shielding effect (such as Shield spell). This bonus does not apply against touch attacks.
"Wait! I forgot I have the Bull's Strength casted on me, so I should add 2 to my Athletics check, which means I successfully climb the tree" yelled Bob the Fighter. However, what Bob also forgot is that he had a gloves of strength +4 on, which shares the same type of modifier as Bull's Strength. Bob still kept his lump on his head.