Bearing Analysis · DWG LS-029

Bearing Friction & Heat

Quick estimate of a rolling bearing's friction moment and the heat it puts into the oil, housing and shaft, using a typical friction coefficient for the bearing type. Bore, type and speed come from your calculation string when active; set the load below.

Maker method (NTN)Last reviewed

Source: NTN catalogue 2203E ch.10 Friction and temperature rise (PDF)

Uses a typical friction coefficient for each bearing type, not a load- and lubricant-dependent friction model.

Validation
  • Matches hand calculations of NTN eqs 10.1–10.2: 6309 (d 45 mm, P 5,000 N, 1,800 rpm, μ 1.25×10⁻³) gives M 140.6 N·mm and 26.58 W (hand: 140.625 N·mm, 26.578 W); 22220 (3.937 in, 10,000 lbf, 900 rpm, μ 2.25×10⁻³) gives 472.9 W (hand: 472.90 W).

How calculators are checked: editorial standards.

Bearing, load & speed
Typical values for normal running conditions. Type a value to override.
The load the bearing carries in service (radial, or axial for thrust bearings), not the catalog rating.
Method, worked example & FAQ

How this calculator works

The friction moment comes from the definition of the friction coefficient, μ = 2M ÷ (P·d), so M = μ × P × d ÷ 2 (NTN eq. 10.1), with M in N·mm, P in N and d = bore in mm. The heat is Q = 0.105 × 10⁻⁶ × M × n kW (NTN eq. 10.2), with n in RPM.

μ comes from NTN Table 10.1 for the bearing type: pick the low end, middle or high end of the range, or type your own value. Results are given in W, kW and BTU/hr, and the moment in N·m, N·mm and lbf·in.

Inputs explained

  • Bearing bore (d): inches or mm. Filled from your calculation string when a bearing is selected.
  • Bearing type: sets the μ range from NTN Table 10.1.
  • Friction coefficient: low, mid or high end of the range, or a custom μ.
  • Speed (n): shaft speed in RPM.
  • Bearing load (P): the load the bearing actually carries in service, in lbf or N (radial, or axial for thrust bearings).

Worked example

A 6309 deep groove ball bearing (45 mm bore) at 1,800 RPM carrying 5,000 N, with the mid-range μ = 1.25 × 10⁻³.

M = 1.25 × 10⁻³ × 5,000 × 45 ÷ 2 = 140.6 N·mm (0.141 N·m). Q = 0.105 × 10⁻⁶ × 140.6 × 1,800 = 0.0266 kW.

Calculator output: heat generated 26.6 W (0.0266 kW, 90.7 BTU/hr), friction moment 140.6 N·mm. Across the deep groove ball range (μ 1.0–1.5 × 10⁻³) the heat is about 21.3–31.9 W.

Reading the result & common mistakes

  • Reading it: the heat is what the lubricant, housing and shaft must remove at steady state. Treat it as a band (low to high μ), not one exact number. It is the input for sizing circulating-oil flow or checking whether a bearing will run hot.
  • Catalogue rating instead of service load: P is the load in service, not the dynamic rating C. Entering C overstates the heat many times over.
  • OD or pitch diameter instead of bore: NTN’s equation uses the bore d.
  • Expecting seal or churning losses: contact seals, overfilled housings and very high speeds add friction this estimate leaves out.
  • Check against reality: compare with measured running temperatures before sizing a cooler.

Next step: size the oil flow needed to carry this heat away in Forced Circulation Oil Flow, or check the oil viscosity at the running temperature in Minimum Required Viscosity (ν₁).

Frequently asked questions

How do you calculate bearing friction torque?

With the simple friction-coefficient method in the NTN catalogue: M = μ × P × d ÷ 2, with M in N·mm, the bearing load P in N and the bore d in mm. A 6309 (45 mm bore) carrying 5,000 N with μ = 1.25 × 10⁻³ has M = 140.6 N·mm.

How much heat does a rolling bearing generate?

The friction heat is Q = 0.105 × 10⁻⁶ × M × n kW, with M in N·mm and n in RPM. The same 6309 at 1,800 RPM makes about 26.6 W, or 90.7 BTU/hr, that the oil, housing and shaft must carry away.

Does this include seal friction or oil churning?

No. The typical friction coefficients are for normal running conditions. Contact seals, too much grease or oil, high speeds and start-up all add friction that this quick estimate does not include. For those cases use the bearing maker’s full friction model.