1. Basic dynamic load rating

1) Bearing service life
When bearings rotate under loading, material flakes from the surfaces of inner and outer rings or rolling elements by fatigue arising from repeated contact stress. This phenomenon is called flaking. The total number of bearing rotations until flaking occurs is regarded as the bearing "(fatigue) service life". "(Fatigue) service life" differs greatly depending upon bearing structures, dimensions, materials, and processing methods. Since this phenomenon results from fatigue distribution in bearing materials themselves, differences in bearing service life should be statistically considered. When a group of identical bearings is rotated under the same conditions, the total number of revolutions until 90% of the bearings are left without flaking (i.e. a service life of 90% reliability) is defined as the basic rating life. In operation at a constant speed, the basic rating life can be expressed in terms of time.

In actual operation, a bearing fails because of not only fatigue, but other factors as well, such as wear, seizure, creeping, fretting, brinelling, cracking etc (ref. Bearing failures and countermeasures). Selecting the proper mounting method and lubricant, as well as the bearing most suitable for the application can minimize these bearing failures.
2) Basic dynamic load rating
The basic dynamic load rating is either pure radial (for radial bearings) or central axial load (for thrust bearings) of constant magnitude in a constant direction, under which the basic rating life of 1 million revolutions can be obtained, when the inner ring rotates while the outer ring is stationary, or vice versa. The basic dynamic load rating, which represents the capacity of a bearing under rolling fatigue, is specified as the basic dynamic radial load rating (Cr) for radial bearings, and basic dynamic axial load rating (Ca) for thrust bearings. These load ratings are listed in the specification table.
3) Dynamic equivalent load
Bearings are used under various operating conditions; however, in most cases, bearings receive radial and axial load combined, while the load magnitude fluctuates during operation. The two are compared by replacing the load applied to the shaft center with one of a constant magnitude and in a specific direction, that yields the same bearing service life as under actual load and rotational speed. This theoretical load is reffered to as the dynamic equivalent load, can be obtained using the equivalent load equation.
4) Basic rating life
The basic rating life in relation to the basic dynamic load rating and dynamic equivalent load can be expressed using equation (3-1). It is convenient to express the basic rating life in terms of time, using equation (3-2), when a bearing is used for operation at a constant speed; and, in terms of mileage (km), using equation (3-3), when a bearing is used in railway rolling stock or automobiles.
(Total revolutions) L10 = (C/P)p (3-1)
(Time) L10h = 106(C/P)p/60n (3-2)
(Running distance) L10s = DL10 (3-3)
where;
  L10 : basic rating life 106 (revolution)
  L10h : basic rating life h
  L10s : basic rating life km
  P : dynamic equivalent load N
  C : basic dynamic load rating N
  n : rotational speed r/min
  p : for ball bearings p=3
    : for roller bearings p=10/3
  D : wheel or tire diameter mm
5) Correction of calculated service life
When the bearing is used under heat, adjust the service life by multiplying the basic dynamic load rating indicated in the Bearing Specification Tables by the temperature adjustment factor.
Values of Temperature Adjustment Factor
Bearing temperature 125 150 175 200 250
Temperature adjustment factor 1 1 0.95 0.90 0.75
For applications where more than one bearing is used, calculate the service life of the entire bearing system.
Equation for Calculation of Service Life of Entire System
where;
L :
Rating life of the entire bearing system
L1,L2,L3 : Rating life of individual bearings
e :
Constant e =10/9for ball bearings
   e = 9/8for roller bearings
If both types of bearings are used, use an average.

 Also, adjust the rating life by using reliability factor a1, bearing characteristic factor a2, and operating condition factor a3.