Bearing regreasing interval & grease quantity calculator
SKF nomogram-fit relubrication interval and grease charge. Bearing geometry and design factor come from your selected bearing when a calculation string is active; adjust the operating corrections below.
How this calculator works
The interval starts from a curve fit of the SKF relubrication-interval nomogram for ball bearings. The speed factor is n·dm: shaft speed n in RPM times the mean bearing diameter dm = (bore + OD) ÷ 2 in millimetres. With L = log₁₀(n·dm), the base interval is t = 10^(−0.532·L² + 3.6931·L − 1.5761) hours.
The base interval is multiplied by the bearing design factor (ball ×1, cylindrical or needle roller ×0.5, tapered or spherical roller ×0.1) and by the operating factors you select for shaft orientation, contamination, vibration, moisture and temperature. The result is capped at 8,760 hours (one year). It is shown in hours below one day, otherwise in whole days, weeks or months, rounded down, where one month is 730 hours. The note under the result gives n·dm, the temperature factor and the raw interval in hours.
The grease charge per relubrication is OD (in) × width (in) × 0.114, in ounces. It depends only on the bearing size, not on speed or conditions.
Inputs explained
- OD, bore and width: inches or millimetres. They fill in automatically when you select a bearing in the bearing lookup. Width is only used for the grease charge.
- Speed (n): shaft speed in RPM.
- Bearing design: Ball ×1 · Cylindrical/Needle ×0.5 · Tapered/Spherical ×0.1.
- Shaft orientation: Horizontal ×1 · 45° angle ×0.5 · Vertical ×0.3.
- Contamination: Light non-abrasive ×1 · Heavy non-abrasive ×0.7 · Light abrasive ×0.4 · Heavy abrasive ×0.2.
- Vibration (velocity, in/s): below 0.2 ×1 · 0.2–0.4 ×0.6 · above 0.4 ×0.3.
- Moisture: RH below 80% ×1 · RH 80–90% ×0.7 · Condensation ×0.4 · Water ×0.1. Condensation or water also shows a note recommending a calcium-sulphonate grease.
- Operating temperature: measured at the hottest ring, not ambient. It defaults to 140 °F when no temperature is carried in. Factor = min(2, 2^(−(T − 60 °C) ÷ 15)).
Worked example
A 6309-size ball bearing (45 mm bore, 100 mm OD, 25 mm wide) at 1,780 RPM. Horizontal shaft, light non-abrasive contamination, vibration below 0.2 in/s, RH below 80%, hottest ring at 160 °F.
| Speed factor | n·dm = 1,780 × (45 + 100) ÷ 2 = 129,050 mm·RPM |
|---|---|
| Temperature factor | 160 °F (71.1 °C) → ×0.60 |
| Raw interval | 1,513 hr ÷ 730 = 2.07 months → shown as 2 months |
| Grease charge | 3.94 in × 0.98 in × 0.114 = 0.44 oz for the calculated 1,513 hr |
| Shot for the shown interval | 0.44 oz × (1,460 hr ÷ 1,513 hr) = 0.43 oz every 2 months (same grease per month) |
Calculator output: Re-grease interval 2 months · Grease charge 0.43 oz · “Rounded to a simple interval: calculated 1,513 hr → shown 2 months (1,460 hr). Shot scaled ×0.97 from 0.44 oz to 0.43 oz, so the grease per month is unchanged.” · “n·dm = 129,050 mm·RPM · temp factor 160 °F → ×0.60 · raw interval 1,513 hr (capped at 8,760 hr / 1 yr).”
Frequently asked questions
How is the bearing regreasing interval calculated?
The calculator fits the SKF relubrication-interval nomogram from the bearing speed factor n·dm (dm = mean of bore and OD) and bearing design, then multiplies by correction factors for shaft orientation, contamination, vibration, moisture and operating temperature. Results are capped at one year (8,760 hours).
How does temperature change the regrease interval?
The temperature factor is 1.0 at 60 °C (140 °F) measured at the hottest ring. The interval halves for every 15 °C (27 °F) hotter and doubles for every 15 °C cooler, up to a maximum of 2× at 45 °C (113 °F) and below.
How much grease should I add per relubrication?
The grease charge uses the common rule of bearing outside diameter × width × 0.114 (inches → ounces), the inch form of the SKF side-replenishment quantity 0.005 × D × B grams. Housing design can change the right amount, so check the OEM recommendation.
Does the bearing type change the regrease interval?
Yes. The nomogram fit is for ball bearings. Cylindrical and needle roller bearings get half that interval, and tapered and spherical roller bearings get one tenth, before the operating factors are applied.