Enter the journal diameter, bearing length, bearing clearance factor, rotational speed, and supported load to determine the bearing oil flow.

Bearing Oil Flow Formula

The following equation is used to calculate the Bearing Oil Flow.

Q = 29.3*10^-9*(L+.0043(W/D))*m*D^2*N

  • Where Q is the bearing oil flow (gallons per minute)
  • L is the bearing length (inches)
  • W is the stead load supported by the bearing (lbs)
  • D is the diameter of the journal (inches)
  • m is the bearing clearance factor
  • N is the rotational speed (RPM)

What is Bearing Oil Flow?


Bearing oil flow is the amount of oil that can pass through the bearings of a machine. The oil, which is used to lubricate and cool the surface of the bearings, must be able to pass through the bearings in order for it to have any effect on them.

Bearing oil flow is an important factor in the life of a bearing. The lubrication prevents friction and wear between the rolling elements and the raceway.

If too little oil is supplied, it will not sufficiently cool the bearings; if too much oil is supplied, it will be drawn through the bearing seals around the shaft.

Oil flow can be measured with a simple oil flow gauge (see image) and should be maintained within certain limits for the bearing to operate at its designed temperature range.

However, many variables affect this measurement, such as hub diameter, the number of blades on the turbine wheel, whether the blade tips are bladed or not, etc. Generally, a typical value for bearing flow should be within 30–60% of the “rated” flow for a given bearing type and application.

Understanding what causes bearing oil flow problems and how to correct them is essential for those involved in bearing repair, inspection, routine maintenance, and life extension programs.