Selection usually runs the other way round from the life formula: you know the load, the speed and how long the machine has to last, and you need to know which bearing clears it. Rearranging L10 = (C/P)³ gives the dynamic rating you must buy — then the catalogue tells you which parts have it.
Every deep-groove ball bearing carries a catalogue rating, C — the constant radial load under which 90% of an identical batch will survive one million revolutions before fatigue. Push a bearing harder than its rated load and life falls off fast: the ISO 281 formula L10 = (C/P)³ × 10⁶ revolutions means doubling the load doesn't halve the life — it cuts it to an eighth.
A 6205 bearing (25 mm bore, C ≈ 14.8 kN) carrying a 2,000 N radial load at 1,800 rpm is rated for about 405 million revolutions — roughly 3,750 hours of continuous running. Halve the load to 1,000 N and the same bearing is rated for over 8× longer, purely from the cube relationship — no other change needed.
They share a bore but not a cross-section. The 6300 (heavy) series uses larger balls in a bigger outer ring, giving substantially higher load ratings for the same shaft — at the cost of a larger housing bore and more radial space.
C (dynamic) governs fatigue life under rotation — it's what the L10 formula uses. C₀ (static) is the load a stationary bearing can take before the balls permanently dent the raceway. A bearing can be adequately sized for running duty and still be damaged by a heavy shock load while parked.
No — it's a statistical rating. 90% of an identical batch, under identical conditions, should reach or exceed this life; 10% will fail sooner, and some will run far longer. It also assumes clean lubrication and normal temperature — contamination or heat cuts real life well below the catalogue number.
Switch the load input to Radial + axial and enter both. The tool computes the equivalent dynamic
load P the ISO 281 way and shows the factors it used. For single-row deep-groove ball
bearings the factors e and Y depend only on the ratio Fa/C₀,
not on the individual part, so they are the same across manufacturers.
An earlier version of this page said combining loads needed per-size catalogue factors and declined to do it. That is true of angular-contact and taper roller bearings, but not of the deep-groove bearings this tool covers — so the calculation is now included.
Only once Fa/Fr exceeds the threshold e (typically
0.22–0.44). Below that, the bearing's existing contact angle carries the thrust and the equivalent load
is simply the radial load — the axial component costs you nothing. Above it,
P = 0.56Fr + YFa and life starts falling with the cube of the result.
Rearrange the life formula: C = P × (L10)^⅓, with L10 in millions of revolutions. The
Size for a target life section does this and then names the smallest bearing in each series that
meets it. Note that demanding higher reliability raises the required C — a 99% requirement needs
about 1.59× the rating of a 90% one for the same life.
This page has changed in 46 archived releases, but each of those was a site-wide pass, so none is attributable to this tool on its own and none is listed here. That is not a claim that the tool never changed — a release that reworked many pages at once may well have altered this one too. The changelog has them.