How does armor affect Armor Class?

No armor

The normal unarmored baseline is:

AC = 10 + Dexterity modifier

A class or species feature can provide another unarmored AC formula.

For example, Barbarian Unarmored Defense and Monk Unarmored Defense use different formulas.

Those are alternative calculations.

They are not normally added on top of armor.

Light armor

Light armor allows the wearer's full Dexterity modifier to contribute.

Examples from the 2014 Basic Rules include:

Padded 11 + Dex Leather 11 + Dex Studded leather 12 + Dex

Padded armor also imposes disadvantage on Stealth checks under its table entry.

A high-Dexterity character often benefits from light armor because there is no +2 Dexterity cap.

Medium armor

Medium armor adds some Dexterity but normally caps the contribution at +2.

Examples include:

Hide 12 + Dex (max +2) Chain shirt 13 + Dex (max +2) Scale mail 14 + Dex (max +2) Breastplate 14 + Dex (max +2) Half plate 15 + Dex (max +2)

Scale mail and half plate impose disadvantage on Stealth checks under the normal table.

A character with Dexterity 18 still adds only +2 to ordinary medium armor unless a specific feature changes the cap.

Heavy armor

Heavy armor provides a fixed AC and normally does not add Dexterity.

2014 Basic Rules examples:

Ring mail AC 14 Chain mail AC 16 Splint AC 17 Plate AC 18

A negative Dexterity modifier also does not reduce those fixed heavy-armor AC values under the normal formula.

Heavy-armor Strength requirements

Some heavy armor lists a Strength requirement.

In the 2014 Basic Rules:

Chain mail → Str 13 Splint → Str 15 Plate → Str 15

If the wearer lacks the listed Strength, speed is reduced by 10 feet unless another feature overrides that rule.

The requirement is not the same thing as armor proficiency.

A character can be proficient with plate and still suffer the speed penalty for insufficient Strength.

Stealth disadvantage

Some armor entries impose disadvantage on Dexterity (Stealth) checks.

This is a property of that armor.

It does not mean all medium armor or all heavy armor uses the same stealth rule by category alone; check the table entry.

Shields

A shield normally grants:

+2 AC

when properly used.

Donning or doffing a shield takes one action in the 2014 Basic Rules.

A shield also has its own proficiency requirement.

Armor proficiency is required for effective use

A character who wears armor they are not proficient with suffers major penalties.

Under the 2014 rule, the character has disadvantage on:

• ability checks involving Strength or Dexterity;
• saving throws involving Strength or Dexterity;
• attack rolls involving Strength or Dexterity;

and cannot cast spells while wearing that armor.

This is far more serious than merely losing proficiency bonus.

Donning and doffing take time

Armor is not generally changed instantly during combat.

2014 timings include:

Light armor → don 1 minute / doff 1 minute Medium armor → don 5 minutes / doff 1 minute Heavy armor → don 10 minutes / doff 5 minutes Shield → don 1 action / doff 1 action

This can matter for:

• sleeping;
• ambushes;
• disguises;
• swimming;
• prison escapes;
• infiltration.

Alternative AC formulas do not all stack

A character may have several ways to determine AC.

For example:

• armor;
• Mage Armor;
• Monk Unarmored Defense;
• Barbarian Unarmored Defense;
• natural armor.

When rules give **different calculations**, choose the applicable calculation rather than adding them together.

A separate bonus such as a shield or shield of faith can stack when its own rules allow it.

Magic armor

Magic armor normally begins with the underlying armor's rules and then adds its magic-item effect.

A +1 suit of plate does not change plate into light armor or remove the normal proficiency requirement unless the item specifically says so.