Calculation Parameters

Based on ISO 281 and bearing manufacturer standards









RPM


hours




Calculation Results

Equivalent Dynamic Load P:
—
Required Dynamic Load Rating C:
—
Temperature Factor fT:
—
Speed Factor fn:
—
Life Factor fL:
—

Bearing Selection Recommendations:

Light Duty: Select bearing with C rating 20-30% above calculated value
Normal Duty: Select bearing with C rating 30-50% above calculated value
Heavy Duty: Select bearing with C rating 50-100% above calculated value
Severe Duty: Consider special bearings or multiple bearing arrangement

How the Calculator Works

Reference Standards

International Standards:

  • ISO 281:2007 – Rolling bearings — Dynamic load ratings and rating life
  • ISO/TS 16281 – Methods for calculating the modified reference rating life
  • ANSI/ABMA Std 9 – Load ratings and fatigue life for ball bearings
  • ANSI/ABMA Std 11 – Load ratings and fatigue life for roller bearings

Basic Dynamic Load Rating

The basic dynamic load rating C is calculated using:

C = P × fL / (fT × a1)

where:

  • C — basic dynamic load rating (N)
  • P — equivalent dynamic bearing load (N)
  • fL — life factor
  • fT — temperature factor
  • a1 — reliability factor

Equivalent Dynamic Load

For combined radial and axial loads:

P = X × Fr + Y × Fa

where X and Y are factors dependent on the Fa/Fr ratio and bearing type.

Life Factor Calculation

The life factor is calculated from the required life:

fL = (L10h × n × 60 / 10⁶)^(1/p)

where p = 3 for ball bearings and p = 10/3 for roller bearings.

Temperature Effects

Operating temperature affects bearing capacity:

  • Up to 150°C (302°F): fT = 1.0
  • 200°C (392°F): fT = 0.90
  • 250°C (482°F): fT = 0.75
  • 300°C (572°F): fT = 0.60

Bearing Type Selection Guide

  • Ball Bearings: High speeds, moderate loads, low friction
  • Cylindrical Roller: High radial loads, moderate speeds
  • Spherical Roller: Heavy loads, misalignment capability
  • Tapered Roller: Combined loads, high stiffness
  • Needle Roller: High radial loads, compact design

Important Considerations

  • Always consider safety factors for critical applications
  • Account for shock loads and vibration
  • Proper lubrication is essential for achieving calculated life
  • Contamination can significantly reduce bearing life
  • Consider bearing arrangement (fixed/floating) for thermal expansion

Usage Examples & Value Selection Guide

Example 1: Electric Motor Bearing

Scenario: 30 kW motor with belt drive

  • Bearing Type: Ball bearing (deep groove)
  • Radial Load: 2500 N (belt tension)
  • Axial Load: 200 N (minor thrust)
  • Speed: 1480 RPM
  • Required Life: 40000 hours
  • Temperature: 70°C
  • Reliability: 90%
  • Result: C ≈ 35 kN → Select 6309 (C = 52.7 kN)
Example 2: Pump Shaft Bearing

Scenario: Centrifugal pump with overhung impeller

  • Bearing Type: Spherical roller bearing
  • Radial Load: 8000 N (impeller weight + hydraulic)
  • Axial Load: 3000 N (thrust load)
  • Speed: 2950 RPM
  • Required Life: 50000 hours
  • Temperature: 85°C
  • Reliability: 95%
  • Result: C ≈ 125 kN → Select 22218 (C = 170 kN)
Example 3: Gearbox Output Shaft

Scenario: Industrial gearbox with heavy radial loads

  • Bearing Type: Tapered roller bearing
  • Radial Load: 15000 N
  • Axial Load: 5000 N (helical gear thrust)
  • Speed: 150 RPM
  • Required Life: 100000 hours
  • Temperature: 90°C
  • Reliability: 98%
  • Result: C ≈ 220 kN → Select 32220 (C = 298 kN)

How to Choose Values

Bearing Type Selection
  • Ball Bearings:
    • Speeds up to 20,000 RPM
    • Light to moderate loads
    • Low friction requirements
    • Fa/Fr < 0.5 typical
  • Cylindrical Roller:
    • High radial loads only
    • No axial load capacity (except NJ, NUP)
    • Allow free axial movement
    • High speed capability
  • Spherical Roller:
    • Very heavy loads
    • Misalignment up to 2°
    • Combined loads OK
    • Lower speed limits
  • Tapered Roller:
    • High combined loads
    • High stiffness needed
    • Usually paired
    • Fa/Fr up to 1.5
Load Calculation Tips
  • Belt Drives: Radial load = 1.5-2.5 × belt tension
  • Gear Drives: Include separating forces and dynamic factors
  • Overhung Loads: Calculate moment loads at bearings
  • Dynamic Factors:
    • Light shock: × 1.2-1.5
    • Moderate shock: × 1.5-2.0
    • Heavy shock: × 2.0-3.0
Life Requirements by Application
  • 8,000-12,000 hours: Household appliances, hand tools
  • 20,000-30,000 hours: 8-hour daily operation machines
  • 40,000-50,000 hours: 16-hour daily operation
  • 60,000-100,000 hours: 24-hour continuous operation
  • 100,000-200,000 hours: Critical equipment, no failures
Temperature Considerations
  • Standard bearings: -30°C to +120°C
  • High-temp bearings: Up to 200°C with special grease
  • Stabilized bearings: Up to 250°C (S1 suffix)
  • Special bearings: Up to 350°C (S2, S3 suffix)
  • Note: Higher temps require special lubricants
Reliability Factor Selection
  • 90% (a1=1.0): Standard industrial applications
  • 95% (a1=0.62): Important equipment
  • 96% (a1=0.53): Critical processes
  • 97% (a1=0.44): Safety-critical
  • 98% (a1=0.33): Aerospace, medical
  • 99% (a1=0.21): Ultra-critical, no failure allowed