Axial Load Bearing: Formula, Easiest Way To Calculate Load & Bearing Capacity

Axial load is one of the most important forces engineers must understand when designing shafts, bearings, gearboxes, pumps, motors, conveyors and rotating machinery.

An axial load acts parallel to the shaft or component’s axis. It is also commonly called thrust load or axial force.

For example, imagine a rotating shaft carrying a propeller. If the propeller pushes the shaft forward or backward, the resulting force along the shaft is an axial load. Similarly, a screw jack, ball screw, pump shaft, gearbox or vertical rotating shaft can experience significant axial forces.

Understanding axial force is essential because excessive thrust can cause:

• Bearing overheating
• Excessive vibration
• Shaft displacement
• Raceway damage
• Premature bearing failure
• Gear misalignment
• Seal damage
• Increased friction
• Catastrophic mechanical failure

A correct axial-load calculation therefore helps engineers select the correct bearing, shaft diameter, housing, lubrication system and safety factor.

According to SKF technical guidance, when a radial bearing is subjected to both radial and axial forces, the actual forces generally need to be converted into an equivalent dynamic bearing load before bearing-life calculations are performed.

1. What Is Axial Load?

An axial load is a force that acts parallel to the longitudinal axis of a component.

For a shaft:

Axial Load = Force acting along the shaft axis

It is usually represented by:

Fa = Axial Load

where:

• Fa = axial force
• Unit = N or kN

For example:

If a shaft experiences a force of 2,000 N along its axis:

Fa = 2,000 N = 2 kN

Simple Example

Consider a horizontal shaft:

← 2 kN | SHAFT | 2 kN →

The forces act along the shaft’s centerline. Therefore, they are axial forces.

Axial load is different from radial load.

• Axial force: parallel to shaft
• Radial load: perpendicular to shaft
• Combined load: axial + radial simultaneously

2. Axial Load vs Radial Load

The easiest way to understand the difference (Axial Load vs Radial Load) is by looking at the direction of force.

Parameter	Axial Load	Radial Force
Direction	Parallel to shaft	Perpendicular to shaft
Common name	Thrust load	Radial force
Symbol	Fa	Fr
Main bearing type	Thrust bearing	Radial bearing
Example	Propeller thrust	Pulley belt load
Main effect	Shaft movement along axis	Shaft bending/displacement
Typical applications	Pumps, screws, gearboxes	Motors, conveyors, rollers

Many real machines experience both forces at the same time.

SKF describes combined loading using the general equivalent-load relationship:

P = XFr + YFa

where P is the equivalent dynamic bearing load and X and Y are bearing-specific load factors.

3. Axial Load Formula

For a simple mechanical system, the basic axial-load relationship is:

Fa = F

where the applied force is directly aligned with the axis.

For an inclined force:

Fa = F cos θ

and the radial component becomes:

Fr = F sin θ

where:

• F = total applied force
• θ = angle between the force and shaft axis
• Fa = axial component
• Fr = radial component

Example

Suppose:

F = 10 kN

and the force acts at:

θ = 30°

Then:

Fa = 10 × cos 30°

Fa ≈ 8.66 kN

The radial component is:

Fr = 10 × sin 30°

Fr = 5 kN

Therefore, the original 10 kN force produces approximately:

• 8.66 kN axial load
• 5 kN radial load

This type of force decomposition is extremely useful when analyzing gears, belt drives, screw mechanisms and angled shafts.

4. Axial Load in Bearings

Bearings are particularly important in axial-load applications.

A bearing may experience:

1. Pure axial load
2. Pure radial load
3. Combined axial and radial load

A thrust bearing is specifically designed to support axial loads.

Examples include:

• Thrust ball bearings
• Cylindrical roller thrust bearings
• Tapered roller thrust bearings
• Spherical roller thrust bearings
• Angular-contact ball bearings
• Deep-groove ball bearings for moderate axial loading

SKF states that for a thrust bearing designed to carry purely axial, centrally applied load, the equivalent dynamic load can be simplified to:

P = Fa

However, a radial bearing subjected to combined loading requires the appropriate bearing-specific factors.

5. Axial Load Capacity

Axial load capacity means the maximum axial force that a bearing or mechanical component can safely support under specified conditions.

It is important to distinguish between:

Static load rating

The static load rating is associated with stationary or very slow-moving loading and permanent deformation considerations.

Dynamic load rating

The dynamic load rating is used for bearing-life calculations under rotation.

For example, NTN lists a 6201C3 deep-groove ball bearing with a radial dynamic load rating of approximately 6.75 kN and static load rating of approximately 2.76 kN in its published specifications.

A larger NTN 6220C3 bearing is listed with approximately 135.9 kN dynamic rating and 93 kN static rating.

These examples demonstrate an important engineering principle:

Bearing capacity depends strongly on bearing size, internal geometry, bearing type and operating conditions.

Never assume that the axial capacity of one bearing can be determined simply from its radial dynamic rating.

6. Bearing Life and Axial Load

One of the most important calculations is bearing life.

The basic ISO-style bearing life equation is:

L10 = (C/P)^p

where:

• L10 = basic rating life in millions of revolutions
• C = basic dynamic load rating
• P = equivalent dynamic bearing load
• p = 3 for ball bearings
• p = 10/3 for roller bearings

SKF documentation identifies the same basic relationship for bearing-life calculations.

Example

Suppose a ball bearing has:

C = 20 kN

and the equivalent load is:

P = 5 kN

Then:

L10 = (20/5)^3

L10 = 4³

L10 = 64 million revolutions

Therefore, the basic rating life is approximately:

64 million revolutions

This is a theoretical rating-life calculation, not a guarantee of actual service life. Lubrication, contamination, installation, misalignment, temperature and other factors can significantly affect actual bearing life.

7. Axial Load Calculation: Practical Step-by-Step Method

When solving an axial-load problem, use the following procedure.

Step 1: Identify the direction of force

Determine whether the force is:

• Axial
• Radial
• Combined

Step 2: Draw a free-body diagram

Show:

• Shaft
• Bearing locations
• Applied forces
• Reaction forces
• Force directions

Step 3: Resolve angled forces

For an angled force:

Fa = F cos θ

Fr = F sin θ

Step 4: Calculate bearing reactions

Use equilibrium equations:

ΣF = 0

and, when necessary:

ΣM = 0

Step 5: Determine equivalent bearing load

For a purely axial thrust bearing:

P = Fa

For combined loading:

P = XFr + YFa

where X and Y must be taken from the bearing manufacturer’s data.

Step 6: Calculate bearing life

Use:

L10 = (C/P)^p

Step 7: Check static capacity

The bearing must also satisfy the manufacturer’s static-load requirements.

Step 8: Apply safety considerations

Consider:

• Shock
• Vibration
• Temperature
• Lubrication
• Misalignment
• Contamination
• Speed
• Installation

8. Worked Axial Load Example

Suppose an industrial shaft carries:

Axial load = 8 kN

and a thrust bearing has:

Dynamic load rating C = 40 kN

Assume the bearing is a ball bearing.

Then:

Fa = 8 kN

For a purely axial thrust-bearing calculation:

P = Fa = 8 kN

The life becomes:

L10 = (40/8)^3

L10 = 5³

L10 = 125 million revolutions

Thus:

Basic rating life = 125 million revolutions

If the machine rotates at 1,000 RPM:

Revolutions per hour = 1,000 × 60

= 60,000 revolutions/hour

Approximate life:

125,000,000 / 60,000

≈ 2,083 hours

This example is simplified and should not be treated as a final engineering design. Real applications require manufacturer-specific load factors, lubrication analysis, temperature assessment and other operating conditions.

9. Axial Load Capacity Comparison

The following values illustrate how published bearing ratings can differ significantly between bearing sizes.

Bearing Example	Bore	Dynamic Rating	Static Rating
NTN 6201C3	12 mm	6.75 kN	2.76 kN
NTN 6020C3	100 mm	66.5 kN	54 kN
NTN 6220C3	100 mm	135.9 kN	93 kN
NTN 6319C3	95 mm	169 kN	119 kN
NTN 6034C3	170 mm	187 kN	172 kN

These are manufacturer-published ratings and are included as reference examples rather than universal axial-capacity values.

Important: Do not read this chart as an axial-load-capacity chart. Bearing manufacturers provide separate axial-load guidance and application limits. NTN, for example, publishes allowable axial-load information for deep-groove and angular-contact bearings.

10. Advantages of Proper Axial Load Management

Correct axial-load analysis provides several advantages.

1. Longer Bearing Life

Correctly sizing the bearing reduces overload and premature fatigue.

2. Better Machine Reliability

A properly designed thrust-support system reduces unexpected shutdowns.

3. Lower Maintenance Cost

Correct load selection can reduce bearing replacement frequency.

4. Improved Safety

Excessive axial force can cause shaft displacement and mechanical damage. Proper analysis reduces these risks.

5. Better Energy Efficiency

Excessive loading can increase friction and power consumption.

6. Better Product Selection

Axial-load calculations help engineers select between thrust bearings, angular-contact bearings and other bearing designs.

11. Disadvantages and Challenges of Axial Loading

Axial loading itself is not necessarily harmful, but excessive or poorly controlled axial loading creates problems.

1. Premature Bearing Failure

Excessive thrust can damage rolling elements and raceways.

2. Increased Friction

Higher load can increase friction and heat generation.

3. Shaft Displacement

Large axial forces can move the shaft from its intended position.

4. Alignment Problems

Axial movement can affect gears, couplings and seals.

5. Lubrication Problems

High loading and temperature can accelerate lubricant degradation.

6. Complex Calculations

Combined axial and radial loading requires manufacturer-specific factors.

12. Where Is Axial Load Used?

Axial loads occur in many engineering applications.

Electric Motors

Motor shafts may experience axial forces because of magnetic forces, coupling arrangements or connected machinery.

Pumps

Pump impellers can generate significant axial thrust.

Gearboxes

Helical and bevel gears can generate axial forces.

Screw Jacks

The primary load is often axial.

Ball Screws

Machine-tool ball screws commonly carry axial forces.

Compressors

Rotating components can generate thrust that must be controlled.

Fans and Propellers

Air or fluid movement can create thrust forces.

Conveyors

Certain conveyor arrangements can produce axial shaft forces.

Machine Tools

Feed mechanisms frequently experience axial forces.

13. Axial Load in Gears

Gear systems are another important source of axial load.

For example, helical gears generate an axial component because the teeth are angled relative to the shaft.

For a simplified gear-force analysis:

Ft = 2T/d

where:

• Ft = tangential force
• T = torque
• d = pitch diameter

Depending on the gear geometry, the axial component can be related to the helix angle.

A simplified relationship is:

Fa = Ft tan β

where:

• Fa = axial force
• Ft = tangential force
• β = helix angle

Example

Suppose:

T = 500 Nm

d = 0.2 m

Then:

Ft = 2 × 500 / 0.2

Ft = 5,000 N

If:

β = 20°

Then:

Fa = 5,000 × tan 20°

Fa ≈ 1,820 N

Therefore, the gear can generate approximately 1.82 kN axial force.

This is why helical-gear systems frequently require bearings capable of supporting axial loads.

14. Axial Load Problem-Solving: Common Problems

Problem 1: Bearing Gets Hot

Possible causes:

• Excessive axial load
• Incorrect bearing selection
• Insufficient lubrication
• Excessive preload
• Misalignment
• Excessive speed

Solution

Measure the actual operating load, calculate the equivalent dynamic load and compare it with manufacturer limits.

Problem 2: Bearing Fails Too Early

Possible causes:

• Axial overload
• Contamination
• Poor lubrication
• Incorrect installation
• Shaft/housing misalignment

Solution

Do not simply replace the bearing with another identical unit. First determine why the original bearing failed.

Problem 3: Shaft Moves Axially

Possible causes:

• Insufficient thrust-bearing support
• Incorrect locating-bearing arrangement
• Excessive thrust
• Incorrect preload
• Housing deformation

Solution

Check the shaft’s axial locating system and verify the bearing arrangement.

Problem 4: Combined Axial and Radial Load

This is one of the most common real-world conditions.

Use:

P = XFr + YFa

The correct X and Y factors depend on the bearing type and manufacturer.

Never assume X = 1 and Y = 1 unless the applicable engineering method specifically permits it.

15. Axial vs Radial vs Combined Load

Feature	Axial	Radial	Combined
Direction	Along axis	Across axis	Both
Common symbol	Fa	Fr	Fa + Fr
Typical bearing	Thrust	Radial	Angular/contact or suitable radial bearing
Main concern	Thrust capacity	Radial capacity	Equivalent dynamic load
Calculation complexity	Low to medium	Low to medium	Medium to high
Common applications	Pumps, screws	Motors, rollers	Gearboxes, pumps

16. How to Choose a Bearing for Axial Load

Before selecting a bearing, determine:

1. Required axial load
2. Radial load
3. Shaft diameter
4. Operating speed
5. Temperature
6. Lubrication method
7. Required service life
8. Shock and vibration
9. Alignment
10. Available installation space

General Selection Guide

High axial load: Consider a thrust bearing.

Combined radial + axial load: Consider an angular-contact or tapered roller bearing depending on application.

Moderate axial load with radial load: A suitable deep-groove ball bearing may be appropriate, subject to manufacturer limits.

Heavy axial and radial loads: Consider tapered or spherical roller-bearing arrangements according to the application.

17. Important Factors Affecting Axial Load Capacity

Axial capacity is not determined by bearing size alone.

Important factors include:

• Bearing geometry
• Contact angle
• Number of rolling elements
• Raceway design
• Internal clearance
• Preload
• Lubrication
• Speed
• Temperature
• Material
• Installation
• Misalignment
• Load direction
• Shock loading

NTN’s technical material provides allowable axial-load information for different bearing families, illustrating why axial capability must be evaluated for the specific bearing design.

18. Powerful Engineering Checklist

Before approving an axial-load design, check:

• Is the axial force correctly identified?
• Is the force direction correct?
• Have angled forces been resolved?
• Have radial and axial forces been separated?
• Is the bearing type appropriate?
• Has equivalent dynamic load been calculated?
• Has bearing life been calculated?
• Has static capacity been checked?
• Has shock loading been considered?
• Is lubrication adequate?
• Is operating temperature acceptable?
• Is shaft alignment correct?
• Is the installation method correct?
• Is an appropriate safety margin included?

19. Key Axial Load Formulas

Basic axial force

Fa = F

Force component

Fa = F cos θ

Radial component

Fr = F sin θ

Bearing equivalent load

P = XFr + YFa

Pure axial thrust-bearing case

P = Fa

Ball-bearing basic life

L10 = (C/P)³

Roller-bearing basic life

L10 = (C/P)^(10/3)

Gear tangential force

Ft = 2T/d

Simplified helical-gear axial force

Fa = Ft tan β

Always use the appropriate manufacturer’s calculation method for the selected bearing.

Conclusion

Axial load is a fundamental mechanical-engineering concept that directly affects bearing selection, shaft design, gearbox reliability and machine life.

The most important principle is simple:

Axial load acts parallel to the shaft axis.

However, real machines rarely experience perfectly isolated forces. Radial and axial loads often occur simultaneously, requiring engineers to calculate an equivalent dynamic bearing load.

For a pure axial thrust-bearing application:

P = Fa

For combined loading:

P = XFr + YFa

Once the equivalent load is known, bearing life can be estimated using the appropriate bearing-life equation.

The correct engineering workflow is therefore:

Identify force → Resolve components → Calculate bearing reactions → Determine equivalent load → Check dynamic rating → Check static rating → Calculate life → Verify lubrication, speed, temperature and installation.

A powerful axial-load design is not simply about choosing the biggest bearing. It is about selecting the right bearing for the actual force, speed, environment, service life and operating conditions.

For engineering design, always use the current manufacturer’s catalog and application limits for the exact bearing model. SKF and NTN both provide detailed technical information for bearing load and life calculations.

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