[Glossary](/glossary.md)/[Gunnery](/glossary/category/gunnery.md)

# Penetration

How much armor a shell can defeat, in millimetres, rolled plus or minus 25 percent on every shot and compared against the effective thickness it hits.

Also known as pen, armor penetration, piercing power.

A [shell](/glossary/shell.md) penetrates when its rolled penetration beats the [effective armor](/glossary/effective-armor.md) at the point of impact. Effective thickness is not what the specification sheet says: the angle of the plate, the shell's [normalization](/glossary/normalization.md) and the distance travelled all change it before the comparison happens.

The plus or minus 25 percent roll is why marginal shots are a lottery. A 220 millimetre gun against 215 effective armor penetrates most of the time and [bounces](/glossary/ricochet.md) often enough to matter, and the same roll is why a shot that should never get through occasionally does.

[Armor-piercing](/glossary/armor-piercing.md) and [APCR](/glossary/apcr.md) shells lose penetration with distance, which is why the value is quoted both at the muzzle and at 500 metres. [HEAT](/glossary/heat.md) and [high explosive](/glossary/high-explosive.md) do not lose any.

## Related terms

[Effective armorThe thickness a shell actually has to defeat once the angle of the plate is accounted for, which is what penetration is compared against.](/glossary/effective-armor.md)[NormalizationThe few degrees a shell turns toward the perpendicular on impact, reducing the effective armor it has to cross.](/glossary/normalization.md)[RicochetA shell deflecting off a plate without any penetration check, which happens beyond 70 degrees for most shells and 85 for HEAT.](/glossary/ricochet.md)[OvermatchThe rule that a shell with a caliber at least three times a plate's thickness cannot ricochet off it, no matter the angle.](/glossary/overmatch.md)[Armor-piercingThe standard solid shell: reliable damage, moderate penetration, five degrees of normalization and a ricochet beyond 70 degrees.](/glossary/armor-piercing.md)

[Every World of Tanks term](/glossary.md)

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