The fatigue life (basic rating life) is the number of revolutions (or number of hours at constant speed) which 90% of a sufficiently large quantity of apparently identical ball bearings will complete or exceed before the first evidence of fatigue develops. The calculations are made according to DIN ISO 281.

Basic rating life in hours is calculated as follows:

Lh =	106    .     (Cr)3
	60 . n       (Pr)

L_n  = basic rating life [h]
n   = speed of inner ring [rpm]
C_r  = basic dynamic radial load [N]
P_r  = dynamic equivalent radial load [N]

Calculation of the dynamic equivalent radial load P_r:

P_r = X . F_r + Y . F_a

P_r   = dynamic equivalent radial load [N]
F_r   = radial load of bearing [N]
F_a  = axial load of bearing [N]
X   = dynamic radial load factor
Y   = dynamic axial load factor

The influence of load on the life is only to be taken into consideration in the above life equation. If the ball bearings listed are used for conventional bearing purposes, this life calculation will be sufficient.

As the life calculation only takes material fatigue as a cause of failure the calculated life will only correspond with the actual life of the ball bearing if the following requirements are fulfilled:

1. Sufficient lubrication is guaranteed during the whole running time.
2. The loads and speeds used in the calculation correspond with the actual operating conditions.
3. Contamination of ball bearings and lubricant is avoided.