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Bearing Speed Limit Checker - ndm Speed Factor & Maximum RPM

Check if your bearing speed is within safe limits based on bearing type, size, and lubrication method

Free bearing speed limit checker that calculates the ndm speed factor (bore diameter in mm × RPM) and compares it against industry-accepted limits for your specific bearing type and lubrication method. Enter the bearing bore diameter, pitch diameter, operating speed, bearing type (deep groove ball, angular contact, cylindrical roller, tapered roller, spherical roller, or thrust ball), and lubrication method (grease, oil bath, oil mist, or oil jet). The calculator returns a risk classification (OK / CAUTION / HIGH) based on how close your operating speed is to the conservative ndm limit. Running bearings above their speed rating generates excess heat, breaks down lubricant, and dramatically shortens bearing life. Grease-lubricated bearings have lower speed limits than oil-lubricated ones because grease cannot carry heat away from the rolling elements as effectively. Oil jet lubrication pushes the limit highest because it provides both cooling and lubrication at the contact zone. The calculator also shows the maximum safe RPM for your bearing configuration so you can evaluate whether a speed increase is feasible with a lubrication change.

Pro Tip: When a bearing runs close to its ndm limit on grease, upgrading to oil mist or oil bath lubrication often doubles the safe speed ceiling. Before redesigning the shaft or buying larger bearings, check whether a lubrication change alone solves the problem. It is almost always cheaper than a mechanical redesign.

Calculate expected bearing life from your load and speed

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Check grease suitability and regreasing intervals

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Start Using This Tool See How It Works

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Bearing Speed Limit Checker
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How It Works

  1. Enter Bearing Dimensions

    Input the bearing bore diameter and pitch diameter (mean of bore and OD) in millimeters. If you only know the bearing number, look up the dimensions from the manufacturer catalog. The pitch diameter drives the ndm calculation.

  2. Select Bearing Type

    Choose from deep groove ball, angular contact ball, cylindrical roller, tapered roller, spherical roller, or thrust ball. Each type has a different speed capability due to internal geometry and rolling element contact dynamics.

  3. Select Lubrication Method

    Choose grease, oil bath, oil mist, or oil jet. Grease has the lowest speed limit. Oil jet has the highest. The speed limit difference between grease and oil jet can be 2 to 3 times for the same bearing.

  4. Enter Operating Speed

    Input the shaft speed in RPM. The calculator multiplies speed by pitch diameter to get ndm, then compares against the limit for your bearing type and lube method.

  5. Review Risk Classification

    Get OK (below 70% of limit), CAUTION (70-90%), or HIGH (above 90%). The calculator shows both the ndm value and the maximum safe RPM so you can evaluate your safety margin.

Built For

  • Maintenance engineers verifying that a motor or pump bearing is running within speed ratings
  • Design engineers selecting bearings for high-speed spindle or blower applications
  • Reliability teams evaluating whether to switch from grease to oil lubrication on problem bearings
  • Millwrights troubleshooting premature bearing failure on high-speed equipment
  • Machine shop personnel checking spindle bearing speed limits before increasing RPM

Frequently Asked Questions

ndm is the bearing pitch diameter in millimeters multiplied by the rotational speed in RPM. It is the standard index used to evaluate whether a bearing is running within its speed capability. Each bearing type and lubrication method has a maximum ndm value above which heat generation exceeds the ability to dissipate it, leading to lubricant breakdown and premature failure.
At high speeds, the main enemy is heat. Grease stays in the bearing and relies on conduction to remove heat, limiting its cooling ability. Oil bath provides better heat removal because oil circulates and carries heat to the housing. Oil mist and oil jet actively inject cool lubricant directly to the contact zone, providing the best cooling and allowing the highest speeds.
The bearing generates more heat than the lubrication system can remove. Temperature rises, lubricant viscosity drops, the oil film thins, and metal-to-metal contact begins. This accelerates wear, causes cage damage, and can lead to seizure. Running 10-20% over the limit may reduce bearing life by 50% or more.
Yes. Deep groove ball bearings and angular contact ball bearings have the highest speed capability. Cylindrical roller bearings are moderate. Tapered and spherical roller bearings have the lowest speed limits because their larger contact areas generate more friction heat. Switching from a spherical roller to a cylindrical roller or ball bearing can significantly increase the speed ceiling, but you must verify that the replacement can handle the load.
Disclaimer: This calculator provides conservative estimates based on published ndm guidelines. Actual bearing speed limits depend on precision class, cage material, internal clearance, and cooling provisions. Always consult the bearing manufacturer catalog for your specific bearing part number. Critical applications should be validated with the bearing manufacturer's engineering support.

Learn More

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Bearing Speed Limits: What ndm Means and Why It Matters

How to check if your bearing is running too fast for the lubrication method, what ndm represents, and what to do when grease cannot keep up with the speed.

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