NIJ and CAST Body Armour Levels & Standards

Bullet proof vests are tested and standardised according to the ammunition they can protect against. This is why vests are referred to according to their level, which is set by the relevant testing agency. For example, in the US the National Institute of Justice (NIJ) is responsible for approving body armour, and is widely considered to be the world leader in testing and grading bullet proof vests. The respective institution in the UK is the Home Office’s Centre for Applied Science and Technology (CAST, formerly HOSDB), which is considered to be the world leader in testing and grading stab and spike proof vests. However, these institutions often share testing methods and equipment, and so armour that meets the standards of one will meet the standards of its equivalent.

NIJ Levels

The NIJ levels for bullet proof armour outline the various strengths and sizes of ammunition that a bullet proof vest can protect against. The higher the level, the stronger the threat it can protect against, and each level is capable of stopping lower level attacks. For example, A Level III vest will protect against ammunition outlined in every preceding level. These levels are as follows:




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)





CAST Levels

CAST levels cover stab and spike proof vests, both of which require additional protection to a bullet proof vest. As mentioned above, CAST is considered to be the world leader in stab and spike testing, but equivalent institutions may meet the same standards. The levels of protection offered by stab proof vests are 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



Of course, spike proof vests are not always the same as stab proof vests, and may require additional protection. They are tested and graded just as all body armour is, and it is important when choosing a vest to make sure that it meets the appropriate testing. Spike protection testing was first introduced to address the threat faced by Prison Officers, and the levels are 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


It is vital that body armour meets the appropriate levels of protection as outlined by the relevant institution. If it does not, it may not offer you the correct protection.