To calculate grease quantity for each lubrication point, establish the component’s replenishment quantity and interval, convert that requirement into volume, and match it to the actual output of the metering device.
For applicable rolling bearings lubricated from the side, the replenishment estimate is G = 0.005 × D × B, with dimensions in millimetres and the result in grams. Pins, bushes and linear guides require their own component-specific lubrication instructions.
For an automatic system, the working calculation is:
Required volume per event = Replenishment mass × Event interval ÷ (Replenishment interval × Grease density)
This determines a preliminary delivery quantity. The permitted dose, interval and delivery conditions must still be checked.
Our starting point is the requirement at each component. A pump can supply the correct total volume while individual points receive too much or too little. The calculation therefore needs to preserve both the quantity and the timing of delivery at every point.
Establish What Each Quantity Represents
Before using a grease quantity, identify whether it describes initial filling, routine replenishment or a separate purging procedure. These quantities serve different purposes.
| Quantity | What It Covers | How to Use It |
|---|---|---|
| Initial component fill | Grease installed during assembly or overhaul | Follow the component’s initial lubrication instructions |
| Replenishment quantity | Grease added during normal service | Pair it with its specified interval |
| Line-filling quantity | Grease required to prime empty tubing and fittings | Account for it during installation or line replacement |
| Purging quantity | Grease used in a specified contamination-removal procedure | Record separately from routine replenishment |
A maintenance entry stating “15 g” is insufficient. A useful entry states 15 g per bearing every 500 operating hours, identifies the grease, and records the source of the requirement.
Also confirm that one lubrication connection represents one component. A fitting feeding a shared housing or several internal passages should not automatically be treated as a single bearing.
Calculate Bearing Replenishment Quantity Within Its Limits
SKF gives the following replenishment relationship for applicable rolling bearings supplied from the side:
G = 0.005 × D × B
Where:
- G = grease replenishment quantity, g.
- D = bearing outside diameter, mm.
- B = total bearing width, mm.
For replenishment through holes in the centre of the inner or outer ring, SKF gives G = 0.002 × D × B. The coefficient depends on the grease entry arrangement; it is not an adjustment factor to choose according to the desired result. Use the specified width or height definitions for tapered roller and thrust bearings. These relationships are described in SKF’s rolling bearing lubrication guidance.
For a side-fed bearing with an outside diameter of 100 mm and a width of 30 mm:
G = 0.005 × 100 × 30 = 15 g
This estimates the replenishment amount. It does not determine the initial housing fill or the replenishment interval.
When the machine manufacturer provides instructions for the actual installation, use those instructions as the primary basis. Housing design and grease flow paths can make a general dimensional estimate inappropriate.
The interval requires a separate assessment of bearing type, speed, load, operating temperature, lubricant and contamination. Bearing calculation tools such as SKF DialSet consider operating conditions alongside component dimensions.
Convert the Requirement Into an Automatic Dose
Assume the bearing above has an independently established requirement of 15 g every 500 operating hours. Also assume:
- Grease density is 0.90 g/cm³, confirmed for the selected lubricant.
- The installation is suitable for smaller, more frequent replenishment.
- A four-hour event interval is being evaluated.
First calculate the average mass rate:
15 ÷ 500 = 0.030 g/h
Then convert mass to volume:
0.030 ÷ 0.90 = 0.0333 cm³/h
Finally calculate the proposed event quantity:
0.0333 × 4 = approximately 0.133 cm³ per event
These are illustrative assumptions, not recommended settings for every bearing of this size.
Use the lubricant’s actual density. NLGI grade describes consistency, not density, and cannot be used to convert grams into cubic centimetres. One millilitre equals one cubic centimetre; one gram does not necessarily equal either.
Equal Average Delivery Does Not Establish Equal Lubrication Performance
The calculation converts an established requirement into a comparable rate. It does not prove that any combination of dose and interval will work.
For example, 0.12 cm³ every two hours and 1.20 cm³ every twenty hours have the same average volume rate. Whether either schedule is suitable depends on the component’s permitted replenishment method and operating conditions.
SKF describes spreading replenishment quantities over an interval for applicable continuous-lubrication arrangements, but this remains application-dependent.
For selection purposes, record three requirements where available:
- Target average delivery.
- Permitted quantity per event.
- Maximum permitted interval between events.
An outlet can match the average demand and still fail the dose or interval requirement. That is why a calculated hourly rate should not be the only acceptance criterion.
Build a Point Schedule Before Selecting Outlets
The following example shows how different component requirements can be compared. All quantities and intervals are hypothetical inputs for demonstrating the method.
Assume the selected grease has a density of 0.90 g/cm³, and a two-hour operating interval has been approved for all four points.
| Point | Component | Established Requirement | Average Volume Demand | Volume Every 2 Hours |
|---|---|---|---|---|
| B1 | Rolling bearing | 5.4 g / 200 h | 0.030 cm³/h | 0.060 cm³ |
| B2 | Rolling bearing | 10.8 g / 200 h | 0.060 cm³/h | 0.120 cm³ |
| B3 | Rolling bearing | 21.6 g / 200 h | 0.120 cm³/h | 0.240 cm³ |
| P1 | Pin-and-bush joint | 7.2 g / 40 h | 0.200 cm³/h | 0.400 cm³ |
| Total | — | — | 0.410 cm³/h | 0.820 cm³ |
For P1, assume the machine manufacturer specifies 7.2 g every 40 operating hours and permits the proposed dosing method:
P1 event volume = 7.2 × 2 ÷ (40 × 0.90) = 0.400 cm³
No bearing formula is applied to the pin. Its established requirement is simply converted into the units needed for metering selection.
The pin receives less grease per original replenishment than B3, but its shorter interval creates a higher average demand. Selecting outlets by comparing replenishment grams alone would reverse their actual requirements.
Why Correct Total Output Can Still Give the Wrong Result
Suppose the total 0.820 cm³ is divided equally among four outlets. Each receives 0.205 cm³ per event.
B1 would receive approximately 3.4 times its target, while P1 would receive only 51% of its target.
The system total would appear correct.
We therefore recommend checking the calculated delivery at every final outlet before accepting the total pump consumption. Reservoir usage is useful for identifying overall changes, but it cannot establish correct point-by-point distribution.
Match Standard Metering Volumes and Calculate the Error
For a metering outlet:
Delivered volume per event = Rated outlet volume × Number of rated discharges
The terms stroke, cycle and sensor pulse must be interpreted according to the specific device documentation. Do not assume they represent the same delivered quantity.
Our progressive divider selection guide lists PFM metering arrangements, including per-outlet volumes and approved combined-outlet configurations. These distinctions matter when translating a point schedule into an assembly.
Return to the earlier bearing requiring approximately 0.133 cm³ every four hours. If the proposed outlet delivers 0.12 cm³ once per event:
Delivered mass rate = 0.12 × 0.90 ÷ 4 = 0.027 g/h
Against the target of 0.030 g/h:
Delivery deviation = (0.027 − 0.030) ÷ 0.030 × 100 = −10%
A −10% deviation is neither automatically acceptable nor automatically unacceptable. It needs an application-based decision and a documented reason.
| Possible Adjustment | What It Changes | What Must Be Checked |
|---|---|---|
| Select another metering volume | Delivery ratio at the affected point | Available configurations and permitted event quantity |
| Change the event interval | Average delivery of the controlled group | Requirements of every point in that group |
| Increase rated discharges per event | Event quantity for connected outlets | Dose limits and effects on all supplied points |
| Create a separate control zone | Allows an independent schedule | Circuit design and control requirements |
A 0.12 cm³ discharge every 3.6 hours mathematically matches the target average rate. However, shortening a shared interval from four hours to 3.6 hours raises delivery to the other points by approximately 11.1%.
Correcting one point by changing the whole circuit is appropriate only when the other points remain within their requirements.
For PFM progressive dividers, the final specification should identify the metering sections and active outlet arrangement, not merely the number of lubrication points.
Separate Delivery Problems From Quantity Problems
A point showing poor lubrication does not necessarily need a larger programmed dose. Check whether the intended quantity is being delivered before changing the demand calculation.
| Observation | What to Investigate Before Changing Quantity |
|---|---|
| One point appears underlubricated | Outlet assignment, line condition, measured discharge and component passage |
| Several points on one branch are affected | Branch supply, divider operation and monitoring feedback |
| A problem begins after line replacement | Priming, air removal, routing and connection errors |
| Grease use rises after a timer change | Actual event count and delivery changes across the controlled group |
| Reservoir consumption is normal but one point is affected | Local distribution; total consumption cannot verify that point |
Longer tubing also does not justify adding its internal volume to every lubrication event.
For example, a 5 m tube with a 4 mm internal diameter holds approximately 62.8 cm³. This is a priming volume, calculated from the tube’s geometry. Once the line is filled, routine point demand remains a separate quantity.
Line length, lubricant pumpability and operating temperature belong in the delivery assessment. They should not be hidden inside an arbitrary increase to the bearing dose.
Verify the Calculated Output at Commissioning
For accessible delivery lines, collecting and weighing grease over a known number of rated discharges provides a useful output check.
Follow the equipment’s isolation and depressurization procedures, prime the line, and collect repeatable discharges in a pre-weighed container. Use enough discharges for the collected mass to be meaningful relative to the balance resolution.
If 20 rated discharges produce 2.16 g:
Mass per discharge = 2.16 ÷ 20 = 0.108 g
At 0.90 g/cm³:
Volume per discharge = 0.108 ÷ 0.90 = 0.120 cm³
This verifies the measured output under the collection conditions. An open-line test does not reproduce the connected component’s resistance or prove that grease is distributed effectively inside the contact.
After reconnection, verify system operation under the intended conditions. Record controller settings, monitoring behaviour, leakage and relevant component-condition observations at comparable load and speed.
A temperature change alone is not a sufficient reason to increase or reduce grease. Review it alongside delivery evidence and the component’s operating condition.
Keep a Record That Can Be Checked Later
The final lubrication schedule should distinguish required delivery, configured delivery and verified delivery.
For each point, retain:
- Component reference and source of its lubrication requirement.
- Grease specification and density used in the calculation.
- Required quantity and interval.
- Selected outlet displacement and rated discharges per event.
- Configured operating interval and calculated deviation.
- Commissioning result and any approved adjustment.
Specify whether the controller counts operating hours or elapsed time. If a machine runs eight hours per day but lubrication continues throughout all twenty-four hours, the delivered quantity per operating hour can differ substantially from the intended calculation.
Frequently Asked Questions
Can one formula calculate grease quantity for every lubrication point?
No. The dimensional bearing formula has a defined application. Pins, bushes, linear guides and other components require their own lubrication instructions or an application-specific assessment. Their established requirements can then be converted into a common delivery rate.
How do I convert grams into grease-gun strokes?
Collect and weigh several complete strokes to establish the gun’s average mass output. Divide the required grease mass by that measured value. Do not transfer a stroke count between guns without checking their output.
Should I round the required quantity up to the next outlet size?
Calculate the resulting delivery deviation first. Then check the permitted dose and interval. Rounding every point upward can create a substantial excess across a multi-point system.
Does more pump pressure mean more grease reaches each point?
For a functioning positive-displacement metering device, the intended quantity is established by displacement and completed discharges. Pressure must be sufficient for delivery, but increasing it does not replace correct metering selection.
Order & Project Support
To assess a lubrication arrangement, provide the point schedule, component references, grease specification, operating duty, minimum startup temperature and line dimensions. Identify any quantities that still require confirmation.
We can use those inputs to review the metering volumes, outlet arrangement and control schedule. Establishing the demand at each point first makes the resulting configuration easier to specify, commission and maintain.