Bullet Resistance, Vitality and Effective HP Explained

Armor stats look like a long list of unrelated numbers. For gunfights, two of them do almost all the work: bullet resistance and vitality. This guide shows how they combine into effective HP, how ammunition and plates change the picture, and how to compare suits fairly.

Effective HP in one formula

Every player has 100 health. The site turns protection into effective HP (EHP), the amount of raw bullet damage needed to kill you:

EHP = 100 × (1 + bullet resistance ÷ 100) × (1 + vitality ÷ 100)

• •100 bullet resistance doubles your EHP to 200.
• •300 bullet resistance gives 400 EHP.
• •Adding 10% vitality to 300 bullet resistance gives 440 EHP.

Bullet resistance and vitality multiply each other, so neither is wasted when you raise the other.

Why vitality gets better on heavy armor

One percent of vitality adds 1 + bullet resistance ÷ 100 points of EHP. With no armor it is worth 1 HP; on a suit with 300 bullet resistance it is worth 4 HP. The relationship is linear, not exponential, but it means vitality artifacts gain value as your armor improves.

Armor-piercing ammunition

Armor piercing (AP) lowers the bullet resistance the attacker sees. Each hit is multiplied by:

100 ÷ (100 + bullet resistance × (1 − AP ÷ 100))

and then divided by 1 + vitality ÷ 100.

For example, 7.62 SBP rounds have 27.5 AP in the current data. Against a Super-Heavy suit at +15 (401.83 bullet resistance), the shooter effectively faces about 291 bullet resistance instead. The SBP round of each caliber is its high-AP option: 15 AP for 9 mm, 20 for 5.45 and 5.56, 27.5 for 7.62 and 30 for 9x39.

Armor plates

Plates are a separate layer. In the site's simulations the default plate is a Ceramic Plate V: 132 durability, absorbing 88% of body-hit damage until it breaks.

• •Head and limb hits bypass the plate completely.
• •Plate penetration on a weapon or ammunition lowers how much the plate absorbs.
• •A few weapons ignore plates entirely in the current data, such as the Gauss Rifle and the CR-72 pistol. Their damage goes straight to health, reduced only by bullet resistance and vitality.

This is why shots-to-kill can change sharply once a plate breaks, and why the TTK Calculator lets you choose the plate.

Which armor stats grow with upgrades

Only bullet resistance changes with an armor's upgrade level. Environmental protections, laceration protection, stability, built-in healing and movement speed stay at their base values at every level.

Most suits list their exact bullet resistance for each level in the game data. For the few that do not, the site estimates +42.6% at +15, rising evenly with each level, and the Wiki page says so.

Examples at +15 from the current data:

• •Super-Heavy suits (Apostle, Reiter, Granite, Chieftain): 401.83
• •SBA TANK: 387.75
• •Centurion: 351.23
• •Albatross Heavy Assault: 340.81

Stability and laceration protection

Hits slow you down. Stability reduces that slow, and 100 stability removes it. The Build Calculator also reports an effective stability that counts laceration protection:

effective stability = (1 − 100 ÷ (100 + laceration) × (1 − stability ÷ 100)) × 100

with stability capped at 100. Neither stat grows with upgrades, so a suit's stability at +0 is its stability at +15.

Comparing two suits fairly

• •Compare suits at the same upgrade level, usually the level you will actually reach.
• •Compare EHP after the ammunition you expect to face, not raw bullet resistance. A gap of 50 bullet resistance shrinks against high-AP rounds.
• •Remember what bullet resistance does not show: movement speed, environmental protection and built-in healing decide whether a suit fits your route.

Check it with the tools

The Build Calculator shows EHP, effective stability and speed for a full loadout as you change it. The TTK Calculator runs repeated fights with real weapons, ammunition and plates, and the DPS Table ranks weapons against a chosen target.