Knowledge · Linear Motion
Calculating the service life of linear guides: formula, example, factors
The nominal service life of a linear guide follows a simple formula, yet two of its terms are regularly misused: the load rating and the reference distance it is tied to. We work through a complete example with real load ratings. The more important part comes after: the separation between the calculated service life and the real one, because contamination, lubrication and mounting decide the real one.
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The formula for nominal service life
For ball rail systems, DIN ISO 14728-1 gives: L10 = (C / P)³ x reference distance. L10 is the nominal service life, C the dynamic load capacity, P the equivalent dynamic load per runner block. The exponent 3 applies to ball guides with point contact; for roller guides with line contact it is 10/3, so life there rises even more steeply with load.
The reference distance is decisive. Bosch Rexroth states the dynamic load capacity as C100, referenced to 100 km of travel. Insert C100 and the life comes out in units of 100 km. Calculate with a rating referenced to 50 km (many competitors) and you must also insert 50 km as the reference distance. Reference distance and load rating belong together, otherwise you misjudge by a factor of 2. Why that is, is explained in sizing a linear guide.
| Term | Meaning |
|---|---|
| L10 | Nominal service life in km of travel that at least 90 percent of guides reach |
| C or C100 | Dynamic load capacity, referenced to 100 km at Bosch Rexroth (DIN ISO 14728-1) |
| P | Equivalent dynamic load per runner block |
| Exponent | Ball: 3 (point contact). Roller: 10/3 (line contact) |
What L10 means
L10 is not a guarantee but a statistical figure. It states: at least 90 percent of a large batch of identical guides reach this travel distance before the first fatigue damage appears at the rolling contact. 10 percent fail earlier, some last a multiple. The 10 in the name stands for that 10 percent failure probability.
For sizing, this means L10 is a solid comparison and dimensioning value, but not a promise for the individual case. If you need higher reliability, size for a longer L10 or add safety through a smaller assumed load.
Worked example: size 25 FNS
Take a guide of size 25 in format FNS with the dynamic load capacity C100 = 28.6 kN (referenced to 100 km, DIN ISO 14728-1, manufacturer data). Let the equivalent dynamic load per block be P = 5 kN. The calculation runs in three steps.
L₁₀ = (C₁₀₀ / P)³ · 100 km
- L₁₀
- nominal service life in km of travel that at least 90 percent of guides reach
- C₁₀₀
- dynamic load capacity in kN, referenced to a 100 km distance at Bosch Rexroth
- P
- equivalent dynamic load per runner block in kN
- ³
- exponent for ball guides with point contact; 10/3 for roller guides
Size 25 FNS, P = 5 kN
- Ratio of rating to load: C₁₀₀ / P = 28.6 kN / 5 kN = 5.72.
- Third power: 5.72³ = 187.1.
- With the reference distance: L₁₀ = 187.1 · 100 km = 18,710 km.
Source: Bosch Rexroth manufacturer data per DIN ISO 14728-1 (C₁₀₀ = 28.6 kN, size 25 FNS), as of 2026-07.
The nominal service life is about 18,700 km of travel. At a mean travel speed of 1 m/s that corresponds to roughly 5,200 operating hours under this load. Keep the terms cleanly separated: kN against kN cancels out, the reference distance supplies the unit km.
L10 calculator: compute the service life directly
Enter the load rating and the load per runner block, choose the reference distance and rolling element: the calculator applies the DIN ISO 14728-1 formula live and converts to operating hours on request.
Enter the load rating and the load per runner block. The reference must match the rating: Rexroth figures are C100; ratings referenced to 50 km calculate with 50 km.
Nominal service life per DIN ISO 14728-1. Real-world life additionally depends on lubrication, contamination, and mounting.
View load ratings in the configuratorConfigure with the load data in view
The PTS configurator shows C100 and C0 directly on every block-format tile. That way you choose size and format with the load ratings in front of you and calculate the life from the real catalog values, instead of hunting them across PDF catalogs.
Prices and stock are visible in the catalog without signing in.
What shortens real service life
In practice, other factors decide whether the guide reaches the calculated L10 or stays far below it. That calculated value applies to ideal conditions: clean, well-lubricated, correctly aligned guides at room temperature.
- Contamination: particles in the rolling contact act like an abrasive and accelerate wear. Wipers, bellows and clean mounting surfaces noticeably extend life.
- Insufficient lubrication: too little or the wrong grease leads to mixed friction and pitting. Relubrication intervals often decide real life more than the calculation does.
- Alignment errors: parallelism and height errors of the rails create internal extra loads that do not appear in the formula and load the guide on top.
- Shock loads and vibration: short peaks load C0 and the contact points more than the mean load P.
- Excessive preload: preload beyond need raises the internal load and lowers life. Choose it by rigidity requirement, not by feel (see [preload on linear guides](/wissen/vorspannung-linearfuehrung)).
Manufacturers correct the calculated life via factors for hardness, temperature, shock and contamination. The exact values of these factors are in the respective manufacturer catalog and apply only to that series. Do not take them from third-party sources or approximation tables. Treat the calculated L10 as a statistical best case and, in practice, plan a reserve downward depending on environment and maintenance discipline.
When the calculation does not hold
Not every application can be sized meaningfully via L10. With very short oscillating strokes, no full lubricant film forms; here standstill marks (false brinelling) threaten instead of classic fatigue wear, and the formula overestimates life. In corrosive or high-purity environments, the material, not the load rating, decides the service life. In these cases the pure calculation misleads, and the sizing belongs in engineering. PTS assesses such cases through the technical request.