Secret Lesson 7

Attack Rolls, Armor Class, Natural 20s, and Natural 1s

You now understand two of the three kinds of D20 Test:

Ability Checks

Saving Throws

The third is the roll used to determine whether an attack successfully strikes its target:

THE ATTACK ROLL

An Attack Roll is a D20 Test.

Its job is simple:

determine whether an attack hits or misses.

The SRD states that an attack hits when the final Attack Roll total equals or exceeds the target’s Armor Class, or AC.

THE BASIC ATTACK ROLL FORMULA

A typical Attack Roll follows this structure:

1d20

+ Relevant Ability Modifier

+ Proficiency Bonus, if applicable

+ Other bonuses or penalties

= Attack Roll Total

Then compare the result with:

TARGET’S ARMOR CLASS

If:

Attack Roll Total ≥ AC

HIT

If:

Attack Roll Total < AC

MISS

SIMPLE EXAMPLE

Your enemy has:

AC 15

You roll:

11

Your Ability Modifier is:

+3

Your Proficiency Bonus is:

+2

So:

11 + 3 + 2 = 16

Since:

16 ≥ 15

the attack hits.

EXAMPLE OF A MISS

Target:

AC 17

Roll:

10

Ability Modifier:

+3

Proficiency Bonus:

+2

Total:

15

Because:

15 < 17

the attack misses.

MATCHING THE AC IS ENOUGH

Just as with a Difficulty Class, you do not need to beat Armor Class.

You only need to meet it.

If the target has:

AC 16

and your final Attack Roll total is:

16

the attack hits.

WHAT DOES ARMOR CLASS REPRESENT?

Armor Class, or AC, represents how difficult a creature is to wound with an attack.

The SRD describes AC as representing how well a creature avoids being wounded in combat.

It is important not to think of AC as only literal armor.

A creature’s AC can reflect several things, including:

  • natural agility

  • armor

  • shields

  • magical protection

  • class features

  • spells

  • magic items

The rules combine these defensive factors into one target number.

ATTACK ROLLS ARE MOST COMMON IN COMBAT

Attack Rolls normally occur during battle.

However, the SRD also notes that a GM can call for an Attack Roll in another situation when appropriate.

Its example is an archery competition.

So the important idea is not:

Attack Roll = only combat

but rather:

Attack Roll = determine whether an attack hits a target.

WHICH ABILITY MODIFIER DO YOU USE?

Different types of attack normally use different abilities.

The SRD gives three broad categories:

Attack Type Ability Normally Used
Melee attack with a weapon Strength
Unarmed Strike Strength
Ranged attack with a weapon Dexterity
Spell attack Determined by the spellcasting feature

 

Let's examine each one.

MELEE WEAPON ATTACKS

A melee attack with a weapon normally uses:

STRENGTH

So a typical melee weapon Attack Roll looks like:

1d20 + Strength Modifier + Proficiency Bonus

provided you are proficient with the weapon.

EXAMPLE — MELEE ATTACK

Your character has:

Strength 16

Therefore:

Strength Modifier +3

Your Proficiency Bonus is:

+2

You attack with a weapon you are proficient with.

You roll:

12

Calculation:

12 + 3 + 2 = 17

If the enemy has:

AC 16

the attack hits.

UNARMED STRIKES

The SRD also lists Unarmed Strikes among attacks that normally use Strength.

The detailed rules for Unarmed Strikes will be covered later when we examine melee combat.

For now, remember:

Unarmed Strike → normally Strength

RANGED WEAPON ATTACKS

A ranged attack with a weapon normally uses:

DEXTERITY

 

So a typical ranged weapon Attack Roll is:

1d20 + Dexterity Modifier + Proficiency Bonus

if you are proficient with that weapon.

EXAMPLE — RANGED ATTACK

Your character has:

Dexterity 18

Therefore:

Dexterity Modifier +4

Proficiency Bonus:

+2

You fire a ranged weapon with which you have proficiency.

You roll:

9

Calculation:

9 + 4 + 2 = 15

If the target has:

AC 14

you hit.

If the target has:

AC 16

you miss.

SPELL ATTACKS

Spell attacks are different.

The ability used for a Spell Attack is determined by the character’s spellcasting feature.

Depending on the spellcasting character, this could involve a different ability.

We will learn this properly when we reach the spellcasting section.

For now:

SPELL ATTACK → USE THE SPELLCASTING ABILITY SPECIFIED BY YOUR FEATURE

SPECIFIC RULES CAN CHANGE THE ABILITY

Remember Lesson 2:

specific exceptions override general rules.

The SRD gives an attack-related example.

Normally:

Melee weapon attack → Strength

But some weapon properties or features can allow another ability to be used.

For example, the Finesse property can allow a weapon to use Strength or Dexterity.

So never assume that the general rule is absolute.

Check the weapon, spell, feature, or other rule being used.

PROFICIENCY BONUS AND ATTACK ROLLS

You add your Proficiency Bonus to an Attack Roll when:

you attack with a weapon you are proficient with

or:

you make a spell attack.

 

This is extremely important.

WEAPON PROFICIENCY

Anyone may be able to wield a weapon, but proficiency determines whether the character adds Proficiency Bonus to the Attack Roll.

If you are proficient:

add Proficiency Bonus.

If you are not:

do not add it.

The detailed weapon proficiency rules will appear later in the course.

EXAMPLE — PROFICIENT WEAPON

Strength Modifier:

+3

Proficiency Bonus:

+2

Roll:

13

Attack Roll:

13 + 3 + 2 = 18

EXAMPLE — SAME WEAPON WITHOUT PROFICIENCY

Strength Modifier:

+3

Roll:

13

But you are not proficient.

Attack Roll:

13 + 3 = 16

The Proficiency Bonus is absent.

SPELL ATTACK PROFICIENCY

The SRD specifies that Proficiency Bonus is also added to spell attacks.

That means a spellcaster’s attack calculation normally includes:

spellcasting Ability Modifier

plus:

Proficiency Bonus

The precise spellcasting formulas will be covered later.

ARMOR CLASS

Now let's examine the number the attacker is trying to reach:

ARMOR CLASS — AC

The Armor Class of a player character is determined during character creation.

A monster’s Armor Class appears in its stat block.

BASE ARMOR CLASS

The SRD gives all creatures the same basic starting formula:

BASE AC = 10 + DEXTERITY MODIFIER

 

For example:

Dexterity Modifier:

+2

Base AC:

10 + 2 = 12

ANOTHER BASE AC EXAMPLE

Dexterity:

18

Dexterity Modifier:

+4

Base AC:

10 + 4 = 14

That is the basic calculation before another rule changes it.

WHAT CAN MODIFY AC?

The SRD notes that Armor Class can then be changed by things such as:

  • armor

  • magic items

  • spells

  • other rules

 

Later lessons will explain exactly how those systems work.

ARMOR CAN CHANGE THE CALCULATION

Different forms of armor can change how AC is determined.

You should therefore not assume that every armored character literally uses:

10 + Dexterity Modifier

as the final value.

That is the basic starting calculation.

An armor rule may provide another AC calculation or modify the result.

We will cover armor fully in:

Lesson 64 — Armor and Shields: Categories, Armor Class, and Armor Training.

SPELLS AND FEATURES CAN ALSO CHANGE AC

A spell or class feature might provide a different method of determining Armor Class.

That creates an important rule:

ONLY ONE BASE AC CALCULATION CAN APPLY

The SRD states that if a creature has several features that each provide a different way to calculate base AC, the creature must choose which calculation to use.

You do not combine multiple base calculations together.

EXAMPLE — TWO BASE AC FORMULAS

Suppose one rule says your base AC is:

10 + Dexterity Modifier

Another feature gives you a different formula.

You do not calculate both and add them together.

Instead:

choose the applicable base AC calculation.

Only one base calculation can be active at a time.

BASE CALCULATION VS. MODIFIER

This distinction will become important later.

A rule that gives you a new base AC calculation is not necessarily the same thing as a rule that gives you:

+1 AC

One changes the formula.

The other modifies the resulting Armor Class.

Always read the wording carefully.

THE ATTACKER ROLLS, THE DEFENDER PROVIDES AC

One useful way to remember the system is:

ATTACKER

Rolls:

Attack Roll

DEFENDER

Has:

Armor Class

Then:

Attack Roll Total vs. AC

That is the basic contest.

NATURAL 20

Now we reach one of the most famous results in the game.

If the actual number shown on the d20 is:

20

before adding any modifiers, this is called a:

NATURAL 20

For an Attack Roll, the SRD states that a Natural 20:

hits regardless of the modifiers or the target’s AC.

It is also a:

CRITICAL HIT

 

WHAT DOES “NATURAL” MEAN?

“Natural” refers to the number shown directly on the die.

Suppose you roll:

20

That is a:

Natural 20

Suppose instead you roll:

17

and add:

+3

giving:

20 total

That is not a Natural 20.

It is:

17 on the die, 20 total.

The distinction matters.

NATURAL 20 EXAMPLE

Enemy AC:

25

Your attack bonus:

+2

You roll:

Natural 20

Normally:

20 + 2 = 22

which would be below AC 25.

But the Natural 20 rule applies.

The attack still hits.

And because it is an Attack Roll Natural 20:

it is a Critical Hit.

CRITICAL HITS

A Natural 20 on an Attack Roll produces a Critical Hit.

Critical Hits affect the attack’s damage.

We will cover their full damage mechanics later when we reach:

Lesson 24 — Hit Points, Damage Rolls, Critical Hits, and Saving Throws Against Damage.

For this lesson, remember:

NATURAL 20 ON AN ATTACK ROLL = AUTOMATIC HIT + CRITICAL HIT

NATURAL 1

The opposite special result is:

NATURAL 1

If you roll a 1 on the d20 for an Attack Roll, the attack misses regardless of your modifiers or the target’s AC.

NATURAL 1 EXAMPLE

Target:

AC 10

Your attack bonus:

+12

You roll:

Natural 1

Mathematically:

1 + 12 = 13

Normally 13 would meet AC 10.

But Natural 1 has a specific rule.

Therefore:

THE ATTACK MISSES

MODIFIERS CANNOT RESCUE A NATURAL 1 ATTACK

For an Attack Roll, no ordinary numerical bonus changes the Natural 1 rule.

Even if your final mathematical total would exceed the target’s AC:

Natural 1 = miss.

This is an example of the specific rules overriding the normal comparison system.

NATURAL 20 AND NATURAL 1 APPLY HERE SPECIFICALLY TO ATTACK ROLLS

This distinction is extremely important.

The SRD wording we are studying specifically states:

Natural 20 on an Attack Roll → hit and Critical Hit

Natural 1 on an Attack Roll → miss

 

Do not automatically assume that every kind of D20 Test uses the same Natural 20 and Natural 1 rules.

Ability Checks and Saving Throws are different types of D20 Test.

Always follow the rules that apply to the specific roll.

IMPORTANT BEGINNER EXAMPLE

Suppose you make an Ability Check against:

DC 25

Your total modifier is:

+2

You roll:

20

Your total is:

22

The Attack Roll rule saying that Natural 20 automatically hits does not turn this Ability Check into an automatic success.

The rule we are studying applies specifically to Attack Rolls.

This is why precise terminology matters.

ATTACK ROLL EXAMPLE FROM START TO FINISH

Your Fighter attacks an enemy.

Enemy:

AC 17

Character:

Strength Modifier +4

Proficiency Bonus +3

The character is proficient with the weapon.

STEP 1 — ROLL THE D20

Result:

12

STEP 2 — ADD THE ABILITY MODIFIER

12 + 4 = 16

STEP 3 — ADD PROFICIENCY

16 + 3 = 19

STEP 4 — COMPARE WITH AC

19 ≥ 17

Result:

HIT

The next step would be determining damage.

SECOND COMPLETE EXAMPLE

Enemy:

AC 18

Attack bonus:

+5

Roll:

11

Total:

16

Since:

16 < 18

MISS

THIRD COMPLETE EXAMPLE — NATURAL 20

Enemy:

AC 30

Roll:

Natural 20

Even if your modifiers do not bring the mathematical total to 30:

HIT

And:

CRITICAL HIT

FOURTH COMPLETE EXAMPLE — NATURAL 1

Enemy:

AC 8

Your attack bonus:

+10

Roll:

Natural 1

Even though:

1 + 10 = 11

and 11 would normally exceed AC 8:

MISS

ATTACK ROLL CHECKLIST

Whenever you make an Attack Roll, follow this process.

STEP 1 — IDENTIFY THE ATTACK

Is it:

  • a melee weapon attack?

  • a ranged weapon attack?

  • an Unarmed Strike?

  • a spell attack?

  • something with a special rule?

STEP 2 — IDENTIFY THE ABILITY

Normally:

Melee weapon / Unarmed Strike → Strength

Ranged weapon → Dexterity

Spell attack → spellcasting ability

Then check whether a specific feature changes that rule.

STEP 3 — CHECK PROFICIENCY

If using a weapon:

Are you proficient with it?

If yes:

add Proficiency Bonus.

Spell attacks also add Proficiency Bonus.

STEP 4 — ROLL THE D20

Check immediately whether the result is:

Natural 20

or:

Natural 1

STEP 5 — APPLY MODIFIERS

Unless the Natural 20 or Natural 1 rule has already determined the attack's hit or miss result, calculate:

d20 + Ability Modifier + Proficiency Bonus + other modifiers

STEP 6 — COMPARE WITH AC

If:

Total ≥ AC

hit.

Otherwise:

miss.

COMMON BEGINNER MISTAKES

MISTAKE 1 — USING DEXTERITY FOR EVERY ATTACK

Ranged weapons normally use Dexterity.

Melee weapon attacks normally use Strength.

Specific properties and features can create exceptions.

MISTAKE 2 — ADDING PROFICIENCY WITHOUT HAVING WEAPON PROFICIENCY

For a weapon Attack Roll, add Proficiency Bonus when you are proficient with that weapon.

MISTAKE 3 — ADDING THE ABILITY SCORE INSTEAD OF THE MODIFIER

If:

Strength 16

then your Strength Modifier is:

+3

You add +3, not +16.

MISTAKE 4 — THINKING AC MEANS ONLY PHYSICAL ARMOR

Armor Class is the target number representing a creature’s defense against attacks.

Many different rules can influence it.

MISTAKE 5 — COMBINING MULTIPLE BASE AC FORMULAS

If several features provide different ways to calculate your base AC:

choose one.

Do not stack the formulas.

MISTAKE 6 — THINKING A TOTAL OF 20 IS A NATURAL 20

A Natural 20 means:

the die itself shows 20.

MISTAKE 7 — APPLYING THE ATTACK-ROLL NATURAL 20 RULE TO EVERY D20 TEST

The rule covered here specifically applies to Attack Rolls.

LESSON 7 — KEY TAKEAWAYS

ATTACK ROLLS DETERMINE WHETHER ATTACKS HIT

Compare the final Attack Roll total with the target’s Armor Class.

THE BASIC FORMULA IS

1d20 + Ability Modifier + applicable Proficiency Bonus + other modifiers

MELEE ATTACKS NORMALLY USE STRENGTH

This includes melee weapon attacks and Unarmed Strikes.

RANGED WEAPON ATTACKS NORMALLY USE DEXTERITY

 

SPELL ATTACKS USE THE SPELLCASTING ABILITY

The relevant spellcasting feature determines which ability applies.

SPECIAL RULES CAN CHANGE THE ABILITY

For example, Finesse can allow Strength or Dexterity with an appropriate weapon.

PROFICIENCY BONUS APPLIES TO PROFICIENT WEAPON ATTACKS AND SPELL ATTACKS

 

ARMOR CLASS IS THE TARGET NUMBER

Attack Total ≥ AC = Hit

BASE AC IS

10 + Dexterity Modifier

unless another rule provides a different calculation.

ONLY ONE BASE AC CALCULATION CAN APPLY

If you have several possible formulas, choose the one you use.

NATURAL 20

For an Attack Roll:

automatic hit

and:

Critical Hit

 

NATURAL 1

For an Attack Roll:

automatic miss

 

NEXT LESSON

LESSON 8 — ADVANTAGE, DISADVANTAGE, REROLLS, AND HEROIC INSPIRATION

So far, every D20 Test has looked like a single d20 roll.

But circumstances can make success more or less likely without simply adding a numerical bonus.

The game handles many of those situations through:

ADVANTAGE

and

DISADVANTAGE

In the next lesson, we will learn:

  • how Advantage works

  • how Disadvantage works

  • why you roll two d20s

  • why multiple sources do not stack

  • what happens when Advantage and Disadvantage occur together

  • how rerolls interact with them

  • what Heroic Inspiration is

  • how Heroic Inspiration is spent

  • how much Heroic Inspiration you can have

  • what happens if you gain it while already having it

SRD 5.2.1 ATTRIBUTION

This work includes material from the System Reference Document 5.2.1 (“SRD 5.2.1”) by Wizards of the Coast LLC, available at https://www.dndbeyond.com/srd. The SRD 5.2.1 is licensed under the Creative Commons Attribution 4.0 International License, available at https://creativecommons.org/licenses/by/4.0/legalcode.