Bearing Equivalent Dynamic Load Calculator

Equivalent dynamic bearing load formula

For a radial bearing under a constant combined radial and axial load, the general catalog-factor equation is:

Symbol	Meaning	Unit
P	Equivalent dynamic radial bearing load	N, kN, or lbf
Fᵣ	Actual radial bearing load	N, kN, or lbf
Fₐ	Actual axial bearing load	N, kN, or lbf
X	Manufacturer catalog radial load factor	dimensionless
Y	Manufacturer catalog axial load factor	dimensionless

The calculator converts both applied loads to canonical newtons, calculates XFᵣ and YFₐ separately, and then displays their sum in the selected result unit.

Safe default: purely radial load

The initial form deliberately uses Fᵣ = 5 kN, Fₐ = 0, X = 1, and Y = 0:

This avoids presenting a bearing-specific combined-load factor as a universal default. It does not prove that a particular bearing can support the load or that P = Fᵣ applies when axial load is present.

Illustrative combined-load example

Suppose a verified bearing product table gives X = 0.56 and Y = 1.63 for the applicable branch, with Fᵣ = 4 kN and Fₐ = 2 kN:

1. Applied load ratio: Fₐ/Fᵣ = 2/4 = 0.5.
2. Radial contribution: XFᵣ = 0.56 × 4 = 2.24 kN.
3. Axial contribution: YFₐ = 1.63 × 2 = 3.26 kN.
4. Equivalent dynamic load: P = 2.24 + 3.26 = 5.5 kN.
5. Axial contribution is 3.26/5.5 = 59.27% of calculated P.

These factor values are illustrative only. They must not be copied to another bearing without confirming its product table, internal design, arrangement, contact angle, load direction, and decision branch.

P is not a vector resultant

Do not replace this equation with √(Fᵣ² + Fₐ²). Equivalent dynamic load is a rating-life equivalence defined by the bearing calculation method, not a geometric resultant force.

The radial and axial loads still act in different directions in the physical bearing system. P is the scalar load used by the applicable rating-life equation after bearing-specific weighting.

Find X, Y, and e in exact product data

For many radial bearings, the applicable equation changes when Fₐ/Fᵣ crosses a limiting factor e. Product tables can provide different X, Y₁, or Y₂ values, and some factors depend on contact angle, relative axial load, internal clearance, or bearing arrangement.

This calculator intentionally asks for X and Y rather than embedding a generic table. Before calculating:

1. identify the exact bearing designation and arrangement;
2. calculate the actual load carried by that bearing;
3. determine Fₐ/Fᵣ in consistent units;
4. use the manufacturer rule to select the correct branch;
5. enter X and Y from that same branch.

If axial load is above zero while Y = 0, the calculator raises a warning because the axial load is being ignored. The warning does not determine the correct factor; it asks for catalog verification.

Pure radial, pure thrust, and excluded cases

SKF states that a constant purely radial load on a radial bearing can be inserted directly as P = F, while a centrically loaded thrust bearing that accommodates only axial load can use P = Fₐ. Schaeffler also identifies bearing types for which the combined radial equation is not applicable.

This V1 calculator requires positive Fᵣ, so it targets radial bearings and does not implement a separate pure-thrust mode. Do not use it for a bearing type whose manufacturer prohibits combined loading or specifies a different equation.

Continue to L10 basic rating life

After verifying P, use the Bearing L10 Basic Rating Life Calculator. The related-action link transfers P and a placeholder 1,200 rpm.

If the application has several repeating load and speed conditions, derive P separately for every constant segment, then combine them with the Bearing Variable Duty Equivalent Dynamic Load Calculator.

The L10 page still requires:

• the manufacturer-published basic dynamic load rating C for the exact bearing;
• the correct ball or roller life exponent;
• the real constant operating speed;
• separate review of lubrication, contamination, mounting, reliability, variable duty, minimum load, and other application conditions.

Engineering scope and limitations

This calculator covers one constant-load equivalent dynamic radial bearing-load equation with user-supplied X and Y factors. It excludes:

• automatic bearing-type identification or catalog-factor lookup;
• selection of the Fₐ/Fᵣ branch, limiting factor e, Y₁, Y₂, or other product-specific coefficients;
• calculation of bearing reactions from shafts, gears, belts, chains, moments, preload, or housing stiffness;
• rotating-ring factors, application factors, shock factors, and load-distribution factors unless already incorporated exactly as the manufacturer method instructs;
• variable loads and speeds, duty-cycle equivalent load, reversals, oscillation, vibration, and transient loads;
• pure-thrust bearing calculations and bearing types that do not permit combined loading;
• equivalent static load P₀, static safety factor, minimum load, skidding, or limiting speed;
• L10 or modified rating life, lubrication, contamination, fatigue load limit, reliability modification, wear, and service-life prediction;
• internal clearance, preload, fits, thermal effects, misalignment, deflection, mounting, sealing, and maintenance;
• catalog selection, dimensional compatibility, availability, cost, warranty, or final application approval.

Use the result only after verifying the exact product-table factors, then complete bearing selection with the manufacturer’s current calculation method and application engineering guidance.

Frequently asked questions

What is equivalent dynamic bearing load P?

P is a hypothetical constant radial load that would have the same influence on bearing rating life as the actual constant radial and axial loads for the applicable bearing method. It is not the vector resultant of Fr and Fa.

How do I choose bearing load factors X and Y?

Use the product table or manufacturer calculation method for the exact bearing designation, arrangement, load direction, and applicable Fa/Fr branch. This calculator does not select X, Y, or the limiting factor e.

When does equivalent dynamic load equal radial load?

For a constant purely radial load on a radial bearing, the applicable manufacturer method may reduce to P = Fr. In this calculator that is represented by X = 1, Y = 0, and Fa = 0.

Why can P be smaller than the radial load Fr?

Some valid catalog branches use X below 1 while an axial contribution is added. Whether that branch applies depends on bearing-specific factors and Fa/Fr limits. A smaller numerical P is not proof that the factors are correct.

Can I use the result in the bearing L10 calculator?

Yes, only after verifying X and Y against the exact bearing data. The handoff transfers P and a placeholder speed; you must enter the exact C rating, select ball or roller type, and replace the placeholder rpm before relying on L10.

References and review status

Reviewed September 1, 2026. References support the equation, terminology, factor-selection workflow, and scope checks; they do not imply endorsement, factor validity for a particular bearing, bearing selection, life prediction, or standards conformity.

• SKF — Railway Technical Handbook — Manufacturer source for the definition of equivalent dynamic bearing load, P = XFr + YFa, factor meanings, pure radial and pure thrust cases, the Fa/Fr limiting-factor concept, and catalog-data requirement.
• Schaeffler — Rolling Bearings, Technical Principles — Independent manufacturer source for equivalent dynamic radial load, X and Y product-table factors, constant versus variable load treatment, and bearing-type exclusions.
• ISO 281:2007 — Rolling bearings — Dynamic load ratings and rating life — Official standard record for the dynamic load-rating and basic rating-life framework in which equivalent dynamic load is used.