Body Armor Protection Levels

It is vital when choosing body armor to make sure that it adheres to the proper protection levels. While there are many different standards for ballistics protection levels, the two most commonly recognized standards for body armor come from the US National Institute of Justice (NIJ) and the UK Centre for Applied Science and Technology (CAST, formerly HOSDB). These are widely held to be the world leaders in standardizing body armor. Testing methods are often shared between the two, so armor that meets the standards of one will meet the requirements of the equivalent.

These standards outline exactly what threats each level of body armor will protect against, as well as the strength of the attack it will stop. This means that a bullet proof vest at Level II for example will not protect against a Level IIIa threat. But what do these levels mean?

Ballistic Levels

Bullet proof vests are designed to ‘trap’ and slow bullets down as they attempt to pass through the vest. Bullet Proof Vests come in two different types; hard and soft. The ‘soft’ armors are designed to protect against most handgun and small arms ammunition, whereas ‘hard’ armors are designed to stop high caliber and armor piercing rounds. The NIJ classifies all armors in the following levels: 

NIJ Levels Ballistic Tables



NIJ Level IIa

NIJ Level II

NIJ Level IIIa


NIJ Level IV


Areal Density

3.5 kg/m

4.2 kg/m

5.9 kg/m

25.9 kg/m

32.5 kg/m















.44 Magnum









7.62mm NATO




.30 Armour Piercing (M2 AP)




Edged Blade Levels

While the NIJ is considered the world standard for ballistics testing, stab-proof vests are standardised by the CAST. Many assume that if a piece of body armor can stop a bullet, it can stop a knife. This is not the case however, and stab proof vests are different in make up to bullet proof vests. It is possible to find multi-threat vests that can protect against both, but these still need to be graded according to the protection they offer against both bullets and edged/spiked weapons. The threat levels for stab proof vests are standardised by the CAST as follows:


  KR1 KR2
  Knife Resistant Level 1 Knife Resistant Level 2
Energy Level E1 E2 E1 E2
Energy (joules)  24 36 33 50
Velocity 5 m/sec 6.2 m/sec 5.9 m/sec 7.3 m/sec
Total Missile Mass 1.9 kg 1.9 kg 1.9 kg 1.9 kg
Maximum Penetration 7mm 20mm 7mm 20mm


Spiked Weapon Levels

There is also spike protection to be considered, which was first introduced into CAST’s standards to address the additional threat faced by Prison Officers. Spike protection can be added to stab and ballistic vests, neither of which will ordinarily protect against spiked weapons. CAST will only certify spike protection in addition to stab protection. The threat levels for spike proof vests are standardised by the CAST as follows:



  KR1 & SP1 KR2 & SP2
  Knife Resistant Level 1 & Spike Protection Level 1 Knife Resistant Level 2 & Spike Protection Level 2
Energy Level E1 E2 E1 E2
Energy (joules)  24 N/A 33 N/A
Velocity 5.0 m/sec N/A 5.9 m/sec N/A
Total Missile Mass 1.9 kg N/A 1.9 kg N/A
Maximum Penetration KR1=7mm, SP1=0mm N/A KR2=7mm, SP2=0mm N/A