What is the n×dm speed factor?

n×dm is the product of rotational speed (RPM) and mean bearing diameter dm = (d+D)/2 in mm. It is a key parameter for assessing whether a bearing can operate at a given speed with grease or oil lubrication.

What are typical n×dm limits for grease lubrication?

For standard grease: DGBB up to 500,000, ACBB up to 450,000, CRB up to 350,000, SRB up to 250,000. With high-speed greases, these limits can increase by 30-50%.

When should I switch from grease to oil lubrication?

Switch to oil when n×dm exceeds the grease limit for your bearing type, typically above 300,000-500,000 for ball bearings. Oil lubrication also allows better heat removal at high speeds.

How does bearing type affect speed limits?

Ball bearings have the highest speed capability due to point contact. Cylindrical roller bearings are next, followed by tapered roller and spherical roller bearings which have the lowest limits due to sliding contact.

Can I exceed the n×dm limit?

Exceeding the limit may work briefly but will lead to excessive heat, grease degradation, cage wear, and premature failure. For high-speed applications, use precision bearings (P5/P4) with proper lubrication.

Free Engineering Tool #053

Bearing Speed Factor n×d_m Calculator

Calculate the n×d_m speed factor and compare against limiting values for grease and oil lubrication by bearing type.

n × dmGrease LimitOil Limit

Results

Speed Factor n × dm

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Grease Limit

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Oil Limit

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Assessment

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Mean Diameter dm

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Speed Factor Formula

Limiting n×dm Values (typical, ×10³)

Bearing Type	Grease Limit	Oil Limit
Deep groove ball (DGBB)	500,000	700,000
Angular contact ball (ACBB)	450,000	650,000
Cylindrical roller (CRB)	350,000	550,000
Tapered roller (TRB)	250,000	400,000
Spherical roller (SRB)	200,000	350,000

Bearing Speed Factor n×dm Calculator | Grease & Oil Limits | Free Online Tool

Published by admin on February 15, 2026 February 15, 2026

Results

Speed Factor Formula

Limiting n×dm Values (typical, ×10³)