Resistant glass is rated based on the level of security it provides. These levels include:

UL752 Level 1 – while this is the lowest level of protection, this type of bullet-resistant glass provides protection against small-calibre handguns. This level can resist a minimum of three bullets fired from a 9 mm and travelling at a speed of 1,175 feet per second.
UL 752 Level 2 – provides protection against bullets fired from larger calibre handguns. This is ideal for establishments that need a slightly higher level of security like banks, jewelry stores, etc. It can withstand a minimum of three rounds of bullets from a .357 magnum soft point travelling at a speed of 1,250 feet per second.
UL 752 Level 3 – provides greater protection for places that need it like government buildings or police stations. Can resist at least three rounds of .44 magnum travelling at a speed of 1,350 feet per second.
UL 752 Level 4 – provides protection against at least one shot fired from a .30 calibre rifle travelling at a minimum of 2,540 feet per second.
UL 752 Level 5 – has the ability to resist one full metal jacket round and provides protection from a 7.62mm rifle travelling at the speed of at least 2,750 feet per second.
UL 752 Level 6 – resists at least five 9mm rounds travelling at a minimum speed of 1,400 feet per second.
UL 752 Level 7 – capable of resisting multiple full metal jacket rounds with 5.56 rifle bullets travelling at a minimum speed of 3,080 feet per second.
UL 752 Level 8 – can resist at least five bullets fired from a 7.62mm rifle.