How much oil flow does my bearing need?
Forced-circulation bearing oil flow calculator. For bearings fed by a circulating oil system: how much oil flow it takes to carry away the bearing’s friction heat at the temperature rise you choose.
NSK heat-balance oil flow rate for the selected bearing, using published friction coefficients per bearing type. Bore and bearing type come from your calculation string when active; set the operating load and oil temperature rise below.
Oiled pillow-block housing · oil in / oil out
Your bearing
Friction coefficient (μ) used for each bearing type
- Deep groove ball 0.0013 · Angular contact ball 0.0015 · Self-aligning ball 0.0010 · Thrust ball 0.0011
- Cylindrical roller 0.0010 · Tapered roller 0.0022 · Spherical roller 0.0028 · Spherical thrust roller 0.0028
- Needle roller (caged) 0.0015 · Full complement needle 0.0025
Approximate values from NSK CAT. E1103, Table 10.1 “Coefficients of Dynamic Friction”.
How hard it works
Don’t know the load? Use the bearing load from the machine maker (OEM) or the design data. This page does not estimate it.
Oil temperatures
A smaller rise needs more oil. Use the rise your lube system is designed for, or the machine maker’s figure.
Your answer
How this calculator works
In plain words: a turning bearing makes heat from friction. The oil flowing through it carries that heat away by warming up between the inlet and the outlet. The less the oil is allowed to warm up, the more oil you need.
Friction heat follows NSK’s friction-torque method: torque M = μ × load × bore ÷ 2, with an approximate friction coefficient μ for each bearing type (NSK CAT. E1103, Eq. 10.1 and Table 10.1). The flow this page reports is
Q (L/min) = 0.19 × 10⁻⁵ × μ × d × n × F ÷ ΔT
where d is the bore in mm, n the speed in RPM, F the load in N and ΔT the oil temperature rise in °C. The constant 0.19 × 10⁻⁵ turns friction power into the oil flow that soaks it up at that rise. Inches, lbf and °F are converted first. Source: NSK Rolling Bearings for Industrial Machinery, CAT. E1103 (PDF).
Worked example
A spherical roller bearing with a 160 mm bore on a roll turning at 500 RPM, carrying 50,000 N. Oil goes in at 45 °C and the system allows it to come out 10 °C warmer.
Inputs: bore 160 mm · bearing type Spherical roller (μ 0.0028) · speed 500 RPM · load 50,000 N · oil in 45 °C · rise 10 °C.
Calculator output: “Set the flow meter to at least 2.13 L/min (0.56 gal/min, about 33.8 gal/hr).” Note line: “ΔT = 10.0°C | μ = 0.0028”.
Check: 0.19 × 10⁻⁵ × 0.0028 × 160 × 500 × 50,000 ÷ 10 = 2.128 L/min.
Frequently asked questions
What temperature rise should I use?
NSK’s catalog (CAT. E1103) does not give a standard rise for this calculation, so this page has no default. Use the rise your lube system was designed for, or the machine maker’s figure. A smaller rise means more oil flow.
Why is this a minimum?
It only counts the bearing’s own friction heat, using a fixed friction coefficient. It leaves out oil churning, seal friction, and heat that comes in from the process or along the shaft, so the real flow needed can be higher.
Where do the friction coefficients come from?
From NSK CAT. E1103, Table 10.1 “Coefficients of Dynamic Friction” (approximate values), for example 0.0013 for deep groove ball bearings and 0.0028 for spherical roller bearings. Open “Friction coefficient (μ) used for each bearing type” under step 1 to see them all.
What about flushing flow?
Flushing, or the machine maker’s lube-system specification, can call for more flow than this. Check the OEM figure and use the higher of the two.