Armor Class (AC) is a fundamental metric in many tabletop role-playing games, most notably in Dungeons & Dragons (D&D). It represents how difficult it is for an attack to hit a character or creature. A higher AC value means a target is more resilient and harder to strike. The AC calculation typically involves a base value, followed by various additions from armor, shields, natural toughness, and magical enhancements, with Dexterity often playing a crucial role.
The Core Formula
The general formula for calculating Armor Class is:
AC = Base AC + Armor Bonus + Shield Bonus + Dexterity Modifier + Natural Armor + Other Bonuses
Let's break down each component:
Base AC: This is the inherent defensive value of a creature or character before any equipment or natural adaptations. In many game systems, this starts at 10 for unarmored, non-monstrous creatures.
Armor Bonus: This comes from the type of armor worn. Different armors offer different levels of protection (e.g., Padded Armor, Leather Armor, Chain Mail, Plate Mail). Heavier armors generally provide higher bonuses but may also impose restrictions.
Shield Bonus: If the character is wielding a shield, this adds a flat bonus to AC. Common shields like bucklers, shields, and tower shields offer increasing AC bonuses.
Dexterity Modifier: Dexterity is an attribute that influences agility and reflexes. For many armors (especially lighter ones), a character's Dexterity modifier is added to their AC, representing their ability to dodge and weave. Heavier armors may limit or negate this bonus.
Natural Armor: Some creatures possess tough hides, scales, or exoskeletons that provide a natural armor bonus. This is inherent to the creature and doesn't require equipment.
Other Bonuses: This category encompasses magical items (like rings of protection or cloaks of protection), spells (such as Shield of Faith), or other situational effects that might increase AC.
Dexterity and Armor Type
It's important to note that the contribution of the Dexterity modifier to AC often depends on the type of armor worn.
Light Armor (e.g., Padded, Leather, Studded Leather): Adds the full Dexterity modifier.
Medium Armor (e.g., Hide, Chain Shirt, Scale Mail, Breastplate, Half Plate): Adds the Dexterity modifier, but only up to a certain maximum (often +2).
Heavy Armor (e.g., Ring Mail, Chain Mail, Splint, Plate): Does not add any Dexterity modifier.
For creatures with Natural Armor, the calculation might be slightly different depending on the specific game rules, but the core principle of adding modifiers remains. The "Base AC" for creatures with Natural Armor often incorporates this natural toughness.
Use Cases
Player Characters: Players use this calculator to determine their character's AC based on their chosen armor, shield, Dexterity score, and any magical gear.
Game Masters (GMs): GMs use it to quickly calculate the AC of monsters and NPCs, ensuring accurate combat encounters.
Character Optimization: Players can experiment with different equipment and attribute builds to find optimal AC values for their characters.
This calculator simplifies the process, allowing you to focus on strategy and gameplay. Always refer to your specific game system's rules for the most accurate interpretation of AC calculation.
function calculateAC() {
var baseAC = parseFloat(document.getElementById("baseAC").value);
var armorBonus = parseFloat(document.getElementById("armorBonus").value);
var shieldBonus = parseFloat(document.getElementById("shieldBonus").value);
var dexterityModifier = parseFloat(document.getElementById("dexterityModifier").value);
var naturalArmor = parseFloat(document.getElementById("naturalArmor").value);
var otherBonuses = parseFloat(document.getElementById("otherBonuses").value);
var resultDiv = document.getElementById("result");
var ac = 0;
// Input validation
if (isNaN(baseAC) || isNaN(armorBonus) || isNaN(shieldBonus) || isNaN(dexterityModifier) || isNaN(naturalArmor) || isNaN(otherBonuses)) {
resultDiv.innerHTML = "Invalid input. Please enter numbers only.";
return;
}
// Basic AC calculation, assuming no armor type restrictions for simplicity in this calculator.
// In a real RPG, specific armor types might limit or negate the Dex modifier.
ac = baseAC + armorBonus + shieldBonus + naturalArmor + otherBonuses;
// Add Dexterity modifier if it's positive, or if it's a negative modifier and the rules allow it (most systems do).
// For simplicity here, we add the modifier directly. In specific game systems,
// heavy armor might negate Dex bonus, and medium armor might cap it.
ac += dexterityModifier;
resultDiv.innerHTML = ac + " Armor Class";
}