AtlasCalcsUtility Calculation Suite
2026-07-30 9 min

Bearing Friction Loss Calculator

Calculate friction torque and power loss in rolling element bearings. Estimate energy losses, heat generation, and efficiency impacts from bearing friction.

Calculator

Bearing Type
Bore d (mm)
Outside Diameter D (mm)
Radial Load F_r (N)
Axial Load F_a (N)
Speed n (RPM)
Lubrication Type
Oil Viscosity (mm\xB2/s)

Results

Normal

Friction Torque M

0.3000N·m

Torque required to overcome bearing friction

Power Loss P_loss

47.12W

Power dissipated as heat in the bearing

Friction Coefficient μ

0.0015-

Effective bearing friction coefficient

Heat Generation

47.12W

Frictional heat generation rate

Energy Cost

$50$/year

Annual electricity cost of bearing friction loss

Visualizations

Results Overview

0.3N·mFriction Torque M
47.1N·mPower Loss P_loss
0N·mFriction Coefficient μ
47.1N·mHeat Generation
50N·mEnergy Cost

Formula

Bearing friction torque is proportional to the friction coefficient, equivalent load, and mean bearing diameter. Power loss is the product of friction torque and angular velocity.

M = 0.5 x μ x F x d_m

Alternative Form

P_loss = M x ω

Variables

SymbolNameUnitDescription
MFriction TorqueN·mTorque resisting bearing rotation
μFriction Coefficient-Effective friction coefficient (depends on bearing type and lubrication)
FEquivalent LoadNCombined radial and axial load on the bearing
d_mMean DiametermmAverage of bore and outside diameter d_m = (d + D)/2
P_lossPower LossWPower dissipated as frictional heat

Explanation

The SKF friction model provides the basis for estimating bearing friction torque. The friction coefficient depends on bearing type, lubrication method, and operating conditions. Cylindrical roller bearings typically have the lowest friction coefficient (0.0011), while angular contact and spherical roller bearings are higher (0.0018). Grease lubrication increases effective friction by approximately 30% compared to oil bath due to churning losses.

Derivation

The friction torque equation M = 0.5 x μ x F x d_m derives from the definition of friction force (F_f = μ x F) acting at the mean bearing radius (r_m = d_m/2). The power loss P_loss = M x ω follows from the definition of mechanical power (rotational torque x angular velocity). These are simplified models; detailed SKF methods include load-dependent, speed-dependent, and drag losses separately.

Step-by-Step Calculation

Follow each step to understand how the result is calculated from your inputs.

Step 1

Calculate the mean bearing diameter d_m = (d + D) / 2 from bore and outside diameter.

Bore d:50.0000 mm
OD D:110.0000 mm
Result: d_m = 80.0000 mm
Step 2

Determine the equivalent bearing load F from radial and axial components.

F_r:5000.0000 N
F_a:1000.0000 N
Result: F = 5000.0000 N
Step 3

Look up the friction coefficient for the bearing type and lubrication method.

Bearing Type:Deep Groove Ball
Lubrication:Oil Bath
Result: μ = 0.0015
Step 4

Calculate friction torque and power loss.

M = 0.5 x μ x F x d_m
μ:0.0015
F:5000.0000 N
d_m:80.0000 mm
Intermediate: M = 0.5 x 0.0015 x 5000.0000 x 80.0000 / 1000
Result: M = 0.3000 N·m, P_loss = 47.12 W
Final Answer
0.3000

Worked Examples

See how the calculator works with different scenarios.

Scenario

A deep groove ball bearing 6208 (d=40 mm, D=80 mm) in an electric motor, radial load 3000 N, axial load 500 N, speed 3000 RPM, oil bath lubrication.

Inputs

Bearing Type:Deep Groove Ball
Bore:40 mm
OD:80 mm
F_r:3000 N
F_a:500 N
Speed:3000 RPM
Lubrication:Oil Bath

Calculation

d_m = (40 + 80)/2 = 60 mm F = max(3000, 0.5x3000 + 0.5x500) = 3000 N μ = 0.0015 (deep groove ball, oil bath) M = 0.5 x 0.0015 x 3000 x 0.060 = 0.135 N·m ω = 3000 x 2π/60 = 314.16 rad/s P = 0.135 x 314.16 = 42.4 W

Result

M = 0.135 N·m, P_loss = 42.4 W

Interpretation

The 42.4 W loss is typical for a 6208 bearing at 3000 RPM. This is a small fraction of motor losses (typically < 1% of motor power). Annual energy cost at continuous operation: $44.60.

Understanding Your Result

Your Result: Friction Torque M: 0.3000 N·m

Typical range: 0.1-10 N·m (general industrial bearings), 10-100 W (small to medium bearings), 100-2000 W (large bearings or high-speed), 0.0010-0.0025 (friction coefficient range for rolling bearings)

What This Means

Friction torque (M) and power loss (P_loss) quantify the energy dissipated as heat in a bearing. Lower values indicate more efficient bearing operation.

Why It Matters

Bearing friction accounts for 5-15% of total mechanical losses in industrial machinery. For a typical 100 kW motor, bearing losses of 100-500 W per bearing add up across multiple bearings in a drive train, affecting overall system efficiency.

Professional Interpretation

The simplified model used here is suitable for initial design estimates. For detailed analysis, use the SKF general bearing friction model which separates load-dependent friction (sliding in contacts), speed-dependent friction (viscous drag), and seal friction. Cylindrical roller bearings have the lowest friction (0.0011) due to pure rolling contact geometry. Deep groove ball bearings (0.0015) balance load capacity with friction. Tapered and spherical roller bearings (0.0018) have higher friction due to sliding components in the roller end/flange contacts.

Recommendations

  • •Use cylindrical roller bearings for pure radial loads to minimize friction
  • •Consider oil mist or minimal quantity lubrication (MQL) for high-speed applications
  • •Switch from grease to oil bath lubrication when power loss is critical
  • •Verify friction coefficients with manufacturer data for critical designs

Educational Content

Introduction

Bearing friction loss is a significant component of total mechanical system losses. Understanding and minimizing bearing friction improves energy efficiency, reduces operating temperatures, and extends lubricant and bearing life.

Concept Explanation

Rolling bearing friction has three main components: load-dependent friction from elastic hysteresis and sliding in the rolling contacts, speed-dependent friction from lubricant viscous drag and churning, and seal friction (for sealed bearings). The total friction torque determines the power required to rotate the bearing and the heat that must be dissipated.

Applications

▸Electric motor efficiency optimization
▸Gearbox bearing selection and power loss estimation
▸Machine tool spindle design
▸Wind turbine gearbox bearing analysis
▸Pump and compressor bearing systems
▸Automotive transmission and wheel bearing efficiency
▸Aerospace actuator bearing loss calculations

Benefits

  • •Reduced energy consumption and operating costs
  • •Lower bearing operating temperatures (longer grease life)
  • •Improved system efficiency (more output power for same input)
  • •Reduced cooling requirements and smaller heat exchangers
  • •Lower lubricant consumption (less thermal degradation)

Limitations

  • •The simplified model does not separate load and speed dependent losses
  • •Seal friction is not included (can be significant for contact seals)
  • •Transient conditions (startup, speed changes) are not modeled
  • •Temperature effects on viscosity and friction are not dynamically calculated

Best Practices

  • •Select the bearing type with the lowest friction coefficient that meets load/life requirements
  • •Use the minimum required lubricant quantity to avoid excess churning losses
  • •Maintain proper oil level in oil bath systems to minimize immersion depth
  • •Verify friction losses through temperature rise measurement during commissioning

Common Misconceptions

Myth: Roller bearings always have lower friction than ball bearings.
Truth: Cylindrical roller bearings have lower friction than ball bearings under pure radial load, but spherical and tapered roller bearings have higher friction than ball bearings due to sliding components in their geometry.
Myth: Bearing friction is constant regardless of speed.
Truth: Friction torque increases with speed due to lubricant churning and drag. The speed-dependent component can exceed the load-dependent component at high speeds, especially with oil bath lubrication.
Myth: Grease lubrication always has higher friction than oil.
Truth: Grease typically has 20-40% higher friction than oil bath at moderate speeds due to churning. However, at very low speeds, grease can have lower friction because there is no oil churning loss.

Practical Tips

  • •Cylindrical roller bearings have the lowest friction coefficient (0.0011) of all rolling bearing types
  • •Oil level in oil bath should reach the center of the lowest rolling element - higher levels increase churning losses
  • •Grease fill quantity dramatically affects friction: 35% fill has 50% less friction than 70% fill
  • •For oil jet lubrication, optimize oil flow rate - excess flow increases drag without additional cooling benefit
  • •Bearing friction generates heat that must be dissipated through the housing and shaft - ensure adequate cooling
  • •The SKF friction model is the industry standard for detailed analysis and is implemented in bearing selection software
  • •Ceramic hybrid bearings (Si3N4 balls/rollers) reduce friction by 20-35% compared to all-steel bearings

Common Mistakes

Using the static friction coefficient instead of the dynamic value
Rolling bearing friction coefficients range from 0.0010 to 0.0025. Values above 0.005 indicate boundary lubrication - reduce load, increase speed, or improve lubrication immediately.
Ignoring lubricant churning losses at high speed
At high speeds (n x d_m > 200,000), churning losses can equal or exceed load-dependent losses. Use oil mist or reduced oil level to minimize these losses.
Neglecting the effect of seal friction
Contact seals (RS, 2RS) add 0.5-5 N x m of friction torque depending on size and speed. For precise power loss estimation, add seal friction from manufacturer data.
Assuming equivalent load equals radial load only
For combined radial and axial loads, use the correct equivalent load formula, which depends on the bearing type. The simplified method of max(F_r, 0.5F_r + 0.5F_a) is a conservative estimate.

Assumptions

This calculator makes the following assumptions to provide estimates:

Simplified Friction Model: Uses a single friction coefficient that combines load and speed effects. The more detailed SKF model separates these contributions.
Steady-State Operation: Assumes constant speed and load. Transient conditions have different friction characteristics.
No Seal Friction: Seal friction is not included. Open bearings (no seals) are assumed. Add manufacturer seal friction data for sealed bearings.
Constant Temperature: Operating temperature is assumed constant. Actual temperature affects viscosity and therefore friction.

Limitations

Be aware of these limitations when using this calculator:

No Speed-Dependent Loss Separation: The model does not distinguish between load-dependent (contact) and speed-dependent (churning) losses, which respond differently to operating changes.
Generic Friction Coefficients: Friction coefficients are generic estimates. Actual values depend on specific bearing design, geometry, and surface finish.
No Thermal Model: Heat generation is calculated but not coupled to a thermal model. Actual temperature rise depends on heat dissipation capacity.
No Starvation Effects: Grease distribution, oil supply rate, and lubricant film formation dynamics are not modeled.

Frequently Asked Questions

Answers to common questions about this calculator.

What is bearing friction torque?
Bearing friction torque (M) is the resistive torque that opposes bearing rotation. It is caused by rolling and sliding friction in the rolling contacts, lubricant viscous drag, and seal friction. It is measured in Newton-meters (N x m) and represents the torque required to rotate the bearing.
How is bearing power loss calculated?
Power loss P_loss = M x omega, where M is the friction torque in N x m and omega is the angular velocity in rad/s (omega = 2 x pi x n / 60, where n is RPM). The result is in Watts.
What is a typical bearing friction coefficient?
Rolling bearing friction coefficients range from 0.0010 to 0.0025: cylindrical roller 0.0011, deep groove ball 0.0015, angular contact ball 0.0018, spherical roller 0.0018, tapered roller 0.0018, needle 0.0013. These values apply under full film lubrication conditions.
Which bearing type has the lowest friction?
Cylindrical roller bearings have the lowest friction coefficient (0.0011) for radial loads. For combined loads, deep groove ball bearings offer a good balance (0.0015). Needle roller bearings also have low friction (0.0013) but are sensitive to misalignment.
How does lubrication method affect bearing friction?
Oil mist lubrication reduces friction by 10-20% compared to oil bath due to lower churning losses. Grease increases friction by 20-40% due to churning. Oil jet can increase friction at high flow rates but provides the best cooling for high-speed applications.
What is the SKF friction model?
The SKF general bearing friction model separates friction into: rolling frictional moment (load-dependent), sliding frictional moment (load-dependent, from roller end/flange contacts), drag frictional moment (speed-dependent, from lubricant churning), and seal frictional moment. Each component is calculated separately for accurate loss estimation.
How does bearing size affect friction?
Friction torque increases with bearing size (d_m^2 approximately). Larger bearings have higher friction torque but not proportionally higher friction coefficient. The mean diameter d_m = (d + D)/2 is the key geometric parameter in the friction torque equation.
What is the effect of load on bearing friction?
Friction torque is approximately proportional to the applied load. Doubling the load roughly doubles the friction torque (and power loss) under constant speed and lubrication conditions. This is why reducing unbalance and misalignment reduces friction losses.
How does speed affect bearing friction losses?
Power loss increases linearly with speed (P = M x omega), but the friction torque M also increases with speed due to lubricant churning. The net effect is P approximately proportional to n^1.5 to n^2 depending on the lubrication method.
What is the difference between rolling and sliding friction in bearings?
Rolling friction occurs at the ball/roller to raceway contact and has very low coefficients (0.0005-0.001). Sliding friction occurs at roller end/flange contacts and cage guidance surfaces with higher coefficients (0.05-0.15). The total bearing friction combines both.
How do ceramic hybrid bearings reduce friction?
Ceramic (Si3N4) balls have 60% lower density than steel, reducing centrifugal forces at high speed. They also have lower surface energy (less adhesion), higher hardness (lower deformation), and better thermal properties (lower expansion), all contributing to 20-35% friction reduction.
What is the optimal oil level for oil bath lubrication?
The optimal oil level reaches the center of the lowest rolling element. Higher levels increase churning losses significantly. The friction torque can be 2-3 times higher at full immersion compared to the optimal level.
How do I reduce bearing friction in an existing system?
Options: 1) Switch from grease to oil bath (20-30% reduction), 2) Reduce oil level to optimal height, 3) Use lower viscosity oil that still provides adequate film thickness, 4) Change to a lower-friction bearing type, 5) Reduce unbalance/misalignment loads.
What is the temperature rise from bearing friction?
Temperature rise = P_loss / (thermal resistance to ambient). For a typical bearing in a cast iron housing, temperature rise is approximately 0.5-2 C per 10 W of loss depending on housing size and cooling. Excess temperature (>90 C) reduces grease life exponentially.
How does oil viscosity affect bearing friction?
Higher viscosity increases churning losses (speed-dependent friction) but provides better film thickness for load-dependent friction reduction. The optimal viscosity balances these effects. The SKF model uses the viscosity ratio kappa = nu / nu_1 to determine the friction regime.
What is the energy saving potential from optimizing bearings?
A typical industrial plant can reduce bearing-related energy losses by 15-30% through proper bearing selection, lubrication, and maintenance. For a plant with 1000 bearings averaging 50 W loss each, this represents 65,700-131,400 kWh/year savings.
How do I measure bearing friction torque experimentally?
Methods: 1) Torque transducer between bearing and load, 2) Power measurement of the drive motor minus calculated windage, 3) Calorimetric measurement of heat generation, 4) Deceleration test (measuring speed decay after power removal). Each method has different accuracy and applicability.
What is the effect of misalignment on bearing friction?
Misalignment increases edge loading, which dramatically increases contact pressure and friction. Even 0.001 rad (0.057 degrees) of misalignment can double the friction torque in cylindrical roller bearings. Self-aligning bearings (spherical roller, CARB) are designed to accommodate misalignment.
How do bearing seals affect friction?
Contact seals (RS) add 0.5-5 N x m of friction torque, which can be significant for small bearings. Non-contact shields (Z, ZZ) add minimal friction (< 0.1 N x m). For energy-optimized applications, use shielded rather than sealed bearings where possible.
What is the friction breakdown in a rolling bearing?
Typical breakdown: 40-60% rolling friction (elastic hysteresis), 20-30% sliding friction (roller end/flange), 10-20% churning drag (lubricant), 5-15% seal friction (if sealed). The proportions vary significantly with bearing type, speed, and lubrication.
How does bearing preload affect friction?
Preload increases internal contact loads, adding constant friction torque even under zero external load. For maximum efficiency, use the minimum preload required for stiffness. Excessive preload can increase friction torque by 50-100%. Displacement preload (spring) is preferred over rigid preload for variable-speed applications.
What is the effect of water contamination on bearing friction?
Water contamination (even 100 ppm) can increase bearing friction by 15-30% by degrading the lubricant film and causing corrosion. Water also accelerates grease degradation, leading to increased friction over time. Maintain water content below 100 ppm for mineral oils.
How does cage design affect bearing friction?
Cage friction comes from sliding contact between the cage and rolling elements. Polymer cages (PA66, PEEK) have lower friction than stamped steel or machined brass cages. Optimized cage designs with rolling element guidance reduce cage friction by 20-40%.
What standards govern bearing friction measurement?
ISO 15312 (bearing friction torque measurement), DIN 51819 (mechanical-dynamic testing of rolling bearings), ASTM D4172 (four-ball wear test - for lubricant friction evaluation). Bearing manufacturers also have internal standards for friction measurement.
How does running-in affect bearing friction?
Running-in reduces friction by 10-30% as surfaces smooth and conform. The initial friction is typically 1.5-2 times the steady-state value. Running-in should be performed at reduced load (30-50% of rated) and moderate speed for 30-120 minutes.
What is the friction of coated bearings?
DLC (diamond-like carbon) coated bearings can reduce friction by 20-50% compared to uncoated steel bearings. The coating reduces adhesion at the contact interface and can operate with minimal lubrication. DLC is particularly effective for boundary and mixed lubrication conditions.
How do I calculate the annual energy cost of bearing friction?
Annual cost = P_loss (W) x operating hours/year x electricity rate ($/kWh) / 1000. For continuous operation (8760 hours/year) at $0.12/kWh: annual cost = P_loss x 1.0512. A 50 W bearing loss costs approximately $52.56/year in electricity.
What is the relationship between bearing friction and noise/vibration?
Increased friction often correlates with higher vibration levels. Friction variations can excite bearing natural frequencies. Monitoring friction torque trends can detect developing problems before vibration levels increase significantly.
How does vacuum operation affect bearing friction?
In vacuum, the absence of convective cooling limits heat dissipation. Special vacuum greases (low outgassing) must be used. Friction coefficients are higher in vacuum due to clean surfaces (no oxide layers). Solid lubricants (MoS2, DLC) are often preferred for space and vacuum applications.

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Glossary

Technical terms used in mortgage calculations explained in plain language.

Churning Loss
Power dissipated by the bearing rotating through lubricant (oil or grease), causing fluid drag and viscous heating.
d_m (Mean Diameter)
Average of bearing bore and outside diameter: d_m = (d + D) / 2. Used in friction torque calculations.
Equivalent Load
Single load value that produces the same friction effect as the combined radial and axial loads.
Friction Torque (M)
Resistive torque that must be overcome to rotate the bearing, measured in N x m.
Power Loss (P_loss)
Rate of energy dissipation as heat due to bearing friction, measured in Watts.
Rolling Friction
Resistance to rolling caused by elastic hysteresis of the rolling elements and raceway deforming under load.
Seal Friction
Additional friction torque from contact between bearing seals (or shields) and the rotating inner ring.
SKF Friction Model
Detailed analytical model separating rolling, sliding, drag, and seal components of bearing friction torque.
Sliding Friction
Friction from sliding contact between roller ends and flanges, and between cage and rolling elements.
Viscosity Ratio (kappa)
Ratio of actual operating viscosity to the minimum required viscosity for adequate lubrication in the SKF friction model.

Authoritative References

Trusted sources and standards referenced by this calculator.

Applicable Standards

ISO 15312DIN 51819ISO 281AGMA 9005ISO 15243ASTM D4172

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Page Information

Last Updated:

2026-07-30

Version:

2.0.0

License:

Free to use for educational and professional purposes.