Bearing Analysis · DWG LS-005

Electric motor bearing greasing calculator

Baldor/NEMA-based relubrication intervals, grease volumes and single-point lubricator (SPL) sizing, with severity and mounting corrections. Based on Baldor MN408 Table 3-1 through 3-4. Intervals are for ball bearings — roller bearings and vertical mounts divide by 2. Large motors often run a roller bearing at the drive end and a ball bearing at the opposite end, so each end gets its own bearing type and its own interval, grease shot and SPL setting.

Maker method (Baldor, SKF)Last reviewed 14 Oct 2026

Source: Baldor-Reliance MN408 (PDF) · SKF Rolling bearings and seals in electric motors and generators (PDF)

Validation

Frame-table grease quantities agree with SKF’s G_p = 0.005·D·B within 2% for the 10 bearing sizes compared (the bearing for each frame was inferred).
Intervals compared with SKF’s relubrication diagram for ball bearings (C/P ≈ 20): within about 10% at 1,200–1,800 rpm; at 3,600 rpm the Baldor intervals are 1.3–2× longer than SKF’s for 210 frames and up.
After the drive-end / opposite-end update, all 960 tested frame, speed, mounting, severity, hours and bearing-type combinations gave the same results as before.

How calculators are checked: editorial standards.

Motor lubrication

NEMA Frame Size

Rated Speed (RPM)

Grease Shot Sized By

Drive End (DE) Bearing Type

Opposite Drive End (ODE) Bearing Type Bearing numbers only label the results. Baldor sizes the grease shot by frame, so the shot is the same at both ends; the type changes the interval.

Mounting Orientation

Service Severity (Baldor Table 3-2)

Operating Hours per Year Used to convert interval hours → calendar time and size SPL.

Normalized Schedule Regrease both ends on the shorter interval The end with the longer interval gets a proportionally smaller shot, so both ends go on one route. Untick to schedule each end on its own.

Normalized schedule — both ends

— hr

≈ — · the shorter of the two end intervals (—)

Independent per-end schedules

Drive end (DE)

Adjusted interval

— hr

≈ — · base — hr

Grease volume / event

— oz

— | —

🔧 Single-Point Lubricator (SPL)

Annual grease at this interval: — ≈ —

Recommended SPL Size

—

Sized for about a 12-month change-out, since motors are often checked only when vibration flags a problem.

Opposite drive end (ODE)

Adjusted interval

— hr

≈ — · base — hr

Grease volume / event

— oz

— | —

🔧 Single-Point Lubricator (SPL)

Annual grease at this interval: — ≈ —

Recommended SPL Size

—

Sized for about a 12-month change-out, since motors are often checked only when vibration flags a problem.

How it works & notes

Interval = Baldor Table 3-1 hours for the frame and speed × the severity multiplier, halved for a roller bearing and halved again for a vertical mount, capped at one year (8,760 hr). Grease shot per event is by frame (Table 3-4).
Each end is worked out on its own: drive end (DE) and opposite drive end (ODE) can be ball or roller. Frame, speed, mounting, severity and hours/year are shared, and so is the grease shot, because Baldor sizes it by frame.
Normalized schedule (on by default): both ends are greased on the shorter of the two intervals so they share one route. The end that would normally go longer gets a smaller shot, scaled by short ÷ long interval, so the grease it gets per year doesn't change. The same holds for a single-point lubricator: it meters by rate, so its setting is the same as on the independent schedule. Untick the option to see each end on its own interval and full shot.
Size by bearing number: each end's number is looked up in the site's bearing data (the same catalogue as Bearing Lookup). Its OD (D) and width (B) give the shot from SKF's replenishment quantity G_p = 0.005·D·B grams (D, B in mm), converted at 28.35 g/oz, and its type sets ball or roller for that end. The interval still uses the Baldor frame and speed table. A number that isn't found falls back to the frame shot.
SPL sizing converts ounces to cc at 31.5 cc/oz and picks the smallest standard size (60/120/250/500 cc) that covers a year — about a 12-month change-out, since motors are often checked only when vibration flags a problem.

Source: Baldor MN408 Tables 3-1 to 3-4 (intervals, severity, grease quantity). Bearing-number shot: SKF, Bearings in electric motors and generators, relubrication quantity G_p = 0.005·D·B (replenishment from the side).

The motor nameplate or the manufacturer's lubrication instructions take precedence over these table values.

Electric motor grease

Prefer a polyurea / EM-formulated grease (typically NLGI 2, ~ISO VG 100). Avoid moly and heavy EP greases on motor bearings.

Open lubricant recommendation (motor duty)

Method, worked example & FAQ

How this calculator works

The base interval comes from the Baldor MN408 relubrication table (Table 3-1). It is set by NEMA frame group and rated speed (3600, 1800, 1200 or 900 RPM) for ball bearings in standard service. The base is multiplied by the service severity factor (Standard ×1.0, Severe ×0.5, Extreme ×0.1). It is then halved for roller bearings and halved again for vertical mounting, and capped at 8,760 hours (one year). Calendar time is the interval divided by your operating hours per year.

The grease volume per relubrication comes from Table 3-4 by frame, in ounces, grams and cubic inches. Annual use is volume per event × (operating hours per year ÷ interval), converted at 31.5 cc per ounce. The single-point lubricator (SPL) recommendation is the smallest standard size (60, 120, 250 or 500 cc) that holds a year of grease, with the monthly discharge to set. Above 500 cc a year, the calculator suggests refills, a multi-point system or centralized lubrication. A short list of electric-motor greases (polyurea / EM-formulated) is shown, with greases from your mill inventory first when one is set.

Inputs explained

NEMA frame size: from 56–140 up to 5000–5800, with the approximate IEC frame shown.
Rated speed: 3600 (2-pole), 1800 (4-pole, default), 1200 (6-pole) or 900 RPM (8-pole).
Bearing type: ball, or roller (half the interval).
Mounting orientation: horizontal, or vertical (half the interval).
Service severity: Standard ×1.0 (8 hrs/day, below 40 °C, clean) · Severe ×0.5 (16+ hrs/day, below 50 °C, moderate dirt) · Extreme ×0.1 (16+ hrs/day, above 50 °C or Class H, heavy contamination).
Operating hours per year: defaults to 8,000. Used for calendar time and SPL sizing.

Worked example

A 280-frame, 1800 RPM motor with ball bearings, mounted horizontally, in severe service, running 8,000 hours a year.

Interval	Base 15,000 hr × 0.5 = 7,500 hr ≈ 11 months
Grease per event	0.61 oz (17 g, 1.20 in³)
Annual grease	0.61 oz × (8,000 ÷ 7,500) = 0.65 oz ≈ 20 cc
SPL	60 cc

Calculator output: Adjusted interval 7,500 hr (≈ ~11 months · base 15,000 hr, ×0.5 Severe service) · Grease volume / event 0.61 oz · Recommended SPL size 60 cc, “A 60 cc SPL set to discharge 1.7 cc/month provides approximately a 1-year service life.”

Frequently asked questions

How often should electric motor bearings be greased?

It depends on frame size, speed and duty. This calculator uses the Baldor MN408 base intervals (for example, 15,000 hours for a 280 frame at 1,800 RPM). It multiplies them by 0.5 for severe or 0.1 for extreme service, halves the interval for roller bearings and again for vertical mounting, and caps it at one year (8,760 hours). Follow the motor maker's schedule when the motor has one.

How much grease should I add to a motor bearing?

The volume per relubrication comes from the frame-size table, from 0.08 oz for 56–140 frames up to 4.70 oz for 5000–5800 frames. A 280 frame gets 0.61 oz (17 g). The calculator also shows the amount in grams and cubic inches.

What size single-point lubricator does a motor need?

The calculator converts annual grease use to cubic centimetres at 31.5 cc per ounce. It then picks the smallest standard SPL size of 60, 120, 250 or 500 cc that lasts about a year and shows the monthly discharge to set. If a year's grease is more than 500 cc, it suggests refills, a multi-point system or centralized lubrication.