Minimum thickness of a window required to withstand a pressure differential can be calculated by the following formula:

Th = thickness, inches
R = unsupported radius, inches
P = pressure differential, psi
MR = modulus of rupture, psi
SF = safety factor (We use SF=4 in our calculations)

Modulus of rupture (MR, psi) of commonly used crystals:
Crystals MR, psi
BaF2 3,900
CaF2 5,300
CdTe 3,200
CsI 820
Fused Silica 7,000
GaAs 20,000
Ge 10,500
KBr 160
KCl 340
KRS-5 4,000
LiF 1,600
MgF2 7,200
NaCl 350
Sapphire 65,000
Si 18,100
ZnSe 8,000
ZnS 14,900
ZnS Cleartran 8,700

To calculate minimum thickness of a window required for a given pressure, click on the link: Thickness Calculator.

DISCLAIMER: The minimum window thickness calculation, also depends on many other factors and should be used for reference purpose only.