Bearing Calculators
Eight calculators for specifying and mounting rolling bearings — rating life, equivalent dynamic load, shaft and housing fits, radial internal clearance, limiting speed and dmn, grease quantity and relubrication interval, designation decoding, and unit conversion. Each one computes from figures you supply from the bearing’s own catalog data, and names the standard behind every value it fills in for you.
Equivalent Dynamic Load
Combined radial and axial load reduced to the single radial load that would do the same damage. Everything downstream — life, speed margin, fit — is computed from P, not from the loads you measured.
P = X·Fr + Y·Fa
ISO 281
L10 Rating Life
The life 90 percent of a large group of identical bearings will reach or exceed under the stated load. It is a statistical basis, not a warranty on the one bearing in your machine.
L10 = (C / P)p · L10h = 106 / (60·n) × L10
ISO 281
Limiting Speed and dmn
Whether the speed is survivable, and what is actually limiting it. Lubrication and seal drag move the answer far more than most speed checks allow for.
dm = (d + D) / 2 · dmn = dm × n
Indicative — confirm against the bearing's own limiting speed
Shaft and Housing Fit
What to machine the seats to for the load case, and the interference or clearance that fit actually produces against a bearing ring — which is not the same as against an ordinary hole.
interference = shaft deviation − bearing bore deviation
ISO 286-2 · ISO 492 Normal class
Radial Internal Clearance
The clearance group before mounting, and roughly what survives the press fit. A bearing with no clearance left after mounting runs hot and fails early, and this is the check that is most often skipped.
residual ≈ initial clearance − (bore expansion + OD compression)
ISO 5753-1 · GB/T 4604
Grease Quantity and Interval
Initial fill, relubrication quantity and roughly how often. Over-greasing is the commonest lubrication fault: the churning heats the bearing more than the friction it was meant to prevent.
G = 0.005 · D · B · tf = K·[14×106/(n·√d) − 4d]
Established practice — verify against the lubricant supplier
Bearing Designation Decoder
Read a bearing number: what type it is, what dimension series, what bore, and what the letters after it change. Type 6204 or 22215 EK and see it broken apart.
type · dimension series · bore code · suffixes
ISO 15 · ISO 355 · ISO 104
Unit Converter
Load ratings in kN, a customer drawing in pounds-force, a torque spec in lbf·ft. Exact factors, not rounded ones.
length · force · torque · pressure · speed · mass
Exact conversion factors
Equivalent Dynamic Load
Combined radial and axial load reduced to the single radial load that would do the same damage. Everything downstream — life, speed margin, fit — is computed from P, not from the loads you measured.
P = X·Fr + Y·Fa
ISO 281
L10 Rating Life
The life 90 percent of a large group of identical bearings will reach or exceed under the stated load. It is a statistical basis, not a warranty on the one bearing in your machine.
L10 = (C / P)p · L10h = 106 / (60·n) × L10
ISO 281
Limiting Speed and dmn
Whether the speed is survivable, and what is actually limiting it. Lubrication and seal drag move the answer far more than most speed checks allow for.
dm = (d + D) / 2 · dmn = dm × n
Indicative — confirm against the bearing's own limiting speed
Shaft and Housing Fit
What to machine the seats to for the load case, and the interference or clearance that fit actually produces against a bearing ring — which is not the same as against an ordinary hole.
interference = shaft deviation − bearing bore deviation
ISO 286-2 · ISO 492 Normal class
Radial Internal Clearance
The clearance group before mounting, and roughly what survives the press fit. A bearing with no clearance left after mounting runs hot and fails early, and this is the check that is most often skipped.
residual ≈ initial clearance − (bore expansion + OD compression)
ISO 5753-1 · GB/T 4604
Grease Quantity and Interval
Initial fill, relubrication quantity and roughly how often. Over-greasing is the commonest lubrication fault: the churning heats the bearing more than the friction it was meant to prevent.
G = 0.005 · D · B · tf = K·[14×106/(n·√d) − 4d]
Established practice — verify against the lubricant supplier
Bearing Designation Decoder
Read a bearing number: what type it is, what dimension series, what bore, and what the letters after it change. Type 6204 or 22215 EK and see it broken apart.
type · dimension series · bore code · suffixes
ISO 15 · ISO 355 · ISO 104
Unit Converter
Load ratings in kN, a customer drawing in pounds-force, a torque spec in lbf·ft. Exact factors, not rounded ones.
length · force · torque · pressure · speed · mass
Exact conversion factors
Questions engineers get wrong about these calculations
Why is my calculated L10 life so much shorter than the machine is expected to last?
Because L10 is not a service life. It is the life that 90 percent of a large population of identical bearings will reach or exceed under a constant load, at a reference set of conditions. A real bearing that is cleanly mounted, correctly fitted and well lubricated commonly runs far past its L10, and one that is contaminated or misaligned rarely reaches it. Use L10 to compare candidate bearings against each other and to size for a duty, not to predict the failure date of the one bearing in front of you.
What load rating should I put into the life calculation — the dynamic one or the static one?
The basic dynamic load rating Cr, for a rotating bearing. The basic static rating C0r governs a different failure: permanent indentation of the raceway in a bearing that is stationary, oscillating very slowly, or taking a shock while stopped. If your bearing spends significant time loaded and not turning, check the static safety factor s0 = C0r / P0 as well; the dynamic calculation says nothing about brinelling.
The shaft is 20 mm and the bearing bore is 20 mm. Why is there interference?
Because a bearing bore is not a nominal 20 mm hole. Under ISO 492 the bore tolerance is one-sided and negative — for a 20 mm Normal-class bearing it is 0 to −10 micrometres, so the bore is always at or under size. Put that against a k5 shaft, whose deviations are +2 to +11 micrometres, and the result is between 2 and 21 micrometres of interference. The same k5 shaft in an ordinary H7 hole would be a clearance fit. This is the single most common error when a bearing fit is taken from a general engineering fit table.
Do I need C3 clearance?
C3 is not a quality upgrade, it is a compensation. Fitting a bearing takes internal clearance out of it: the interference on the shaft expands the inner ring, the housing fit compresses the outer ring, and a temperature difference between the two rings takes out more. If the sum of those exceeds what CN started with, the bearing runs preloaded and hot. Specify C3 when you have a heavy interference fit, a hot inner ring, an aluminum housing, or a high speed — and CN when you do not, because unnecessary clearance costs you stiffness and adds noise.
How much grease should go into the bearing?
About a third of the free space inside the bearing for normal speeds, and less at high speed. G = 0.005 · D · B grams, with D and B in millimetres, gets you close. The failure mode people do not expect is over-greasing: a full bearing churns the grease it cannot displace, and the heat that generates does more damage than the friction the grease was there to prevent. The housing around it is a separate decision — 30 to 50 percent full at moderate speed, 20 to 30 percent above half the limiting speed.
The bearing is well under its limiting speed but still runs hot. What did the speed check miss?
Usually the seals, the lubrication method, or the fit. A catalog limiting speed is quoted for an open bearing with adequate lubrication; contact seals rub, and a 2RS bearing can be limited to little more than half that figure. Grease lubrication is lower than oil bath, which is lower than oil mist. And a housing fit that is too tight, or an inner ring that has been pressed on hard, removes the internal clearance the bearing needs at temperature — which shows up as heat long before it shows up as noise.
What does the "e" value in the equivalent load calculation actually decide?
Whether the axial load is doing anything. Below Fa/Fr = e the axial load is small enough that the bearing carries it without changing how the radial load is distributed, so P is just Fr. Above e the load zone shifts and both components matter, so P becomes X·Fr + Y·Fa. For a deep groove ball bearing e is not a constant — it moves with the ratio of the axial load to the static rating, which is why that calculator asks for C0r and the fixed-angle ones do not.