Diablo 1 game mechanics deep dive: combat formulas for to-hit, damage, armor class, spell damage scaling, blocking, resistances, and attack speed — all from Jarulf's Guide.

To Hit (Chance to Hit)

Unlike D2 where high-level characters almost always hit, D1's to-hit formula means you can miss frequently even at max level. The formula for Player vs Monster melee:

Clamped between 5% minimum and 95% maximum. You can never guarantee a hit or miss.

• Dexterity adds half its value to hit chance
• Character level adds directly — higher level = more accurate
• Monster AC subtracts — armored monsters are harder to hit
• Items with "+% To Hit" are extremely valuable in D1

For Monster vs Player, the formula is different: 30 + ToHitmonster - ACplayer/5 - 2·clvl. Your AC is divided by 5, making it far less effective than you'd expect. This is why even high-AC Warriors get hit often in Hell.

Armor Class

AC in D1 reduces the enemy's chance to hit you, but it's divided by 5 in the monster-vs-player formula. So 100 AC only gives -20 to the monster's hit chance. AC is useful but not the god stat it seems.

Dexterity contributes directly to AC. For Rogues this is huge — pumping Dex increases both damage AND defense.

Melee Damage

Melee damage depends on Strength and character level:

Key points:

• Strength × Level multiplies weapon damage — both stats matter enormously
• "+% Damage" items (like "King's" prefix) multiply the final result — stacking these is how Warriors reach insane damage
• Bow damage uses Dexterity instead of Strength in the formula
• Critical hits deal double damage — character level determines crit chance

Blocking

If you have a shield equipped and aren't casting a spell, you have a chance to block incoming melee attacks:

Monster level reduces block chance significantly. In Hell difficulty, blocking becomes much less reliable against high-level monsters. Blocking does NOT work against spells or ranged attacks — only melee.

Spell Damage Scaling

Each spell behaves differently, but all scale with character level and spell level:

slvl = spell level, clvl = character level. The Magic attribute governs mana and cast requirements, not spell damage. See Jarulf's Guide Chapter 4 for the exact per-spell formulas.

Resistances

D1 has three resistance types: Fire, Lightning, and Magic. Each caps at 75% damage reduction. There is no Cold or Poison resistance.

• Difficulty penalty: Normal = 0, Nightmare = -20%, Hell = -40% to all resists
• This means in Hell, you need 115% resist from gear to cap at 75%
• "Obsidian" prefix (+20-40% resist all) is the most valuable prefix for this reason
• Monsters can be immune to damage types (resistance = 100%). Unlike D2, you cannot break immunities

Attack Speed

Each weapon type has a base speed measured in frames. The game runs at ~20 FPS. Faster weapons attack more frequently:

The "of Haste" suffix and unique item speed bonuses reduce frames by a fixed amount. Warriors swing swords the fastest — that's why King's Sword of Haste is the endgame weapon.

Item Generation

When a monster drops an item, the game rolls in order:

1. Item type — based on monster type and dungeon level
2. Quality — normal, magic, or unique (based on mlvl and qlvl)
3. Prefix/Suffix — random from eligible pool based on qlvl

ilvl = mlvl (item level equals monster level). Higher dungeon floors = higher mlvl = access to better prefixes, suffixes, and uniques. This is why farming Hell floors 15-16 yields the best loot.

Key Differences from D2