GURPS Explosive Damage Calculator | 4e Rules Tool

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GURPS Explosive Calc

Damage & Distance Tool (4th Edition)

Explosion Formula
d × +
Example: 6d × 4 (C4 Block)
Distance from Center 2 yds
Target DR (Armor)
Impact Analysis TYPE: CRUSHING EX
0
Effective Damage
Base Damage (At 0 yds) 0
Injury (After DR) 0 HP
Knockback 0 yds
Note: At 0 yards (Contact), targets take full damage. At >0 yards, damage is divided by (3 × Distance).

How Explosions Work in GURPS 4e

Explosives in GURPS don't just deal a flat number to everyone in the room. They follow a realistic (and mathematically intense) inverse-distance law. This calculator handles the division so you can focus on the roleplay.

💡 The Golden Rule: 3x Distance

Unless it is a contact explosion, damage drops off rapidly. The formula is: Damage = Base Damage / (3 × Yards).

This means a grenade doing 24 damage at the center only does 8 damage at 1 yard, and 4 damage at 2 yards. Being just a few steps away saves lives.

Contact vs. Internal Explosions

  • Contact (0 Yards): If the explosive is touching the target (e.g., a limpet mine), they take full Base Damage.
  • Internal: If an explosive goes off inside a target (e.g., swallowed), the damage is multiplied (usually x5 for flesh), creating devastating injury with no DR protection for internal organs.

Knockback Mechanics

Explosions deal Crushing (cr ex) damage by default. Crushing attacks cause 1 yard of knockback for every full 8 points of damage taken (before DR/Armor). If a character is knocked back into a wall, they take additional damage based on velocity.

Frequently Asked Questions

What about fragmentation? +
Fragmentation is calculated separately. It usually attacks with a Skill level of 15 vs specific hit locations. Fragmentation damage does not drop off with distance; you are either hit by a shard or you aren't.
Does cover help? +
Yes. If you are behind cover, the cover's DR subtracts from the blast damage before it hits you. If the damage exceeds the cover's HP/DR, the remaining damage blows through.
How do I calculate TNT equivalent? +
In GURPS, standard TNT does 6d × sqrt(lbs) damage. For example, 1 lb of TNT does 6d damage. 4 lbs does 12d (6d × 2). Modern plastics (C4) usually have a multiplier of 1.4x relative to TNT.

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