The Fatigue Limit Estimation Calculator is a practical online engineering tool designed to help mechanical engineers, material scientists, and manufacturing professionals estimate material endurance limits and evaluate fatigue performance under cyclic loading conditions. Using ultimate tensile strength, surface finish, component size, loading type, and reliability factors, this calculator applies the Marin modification method to estimate fatigue limits for applicable materials. It also supports Goodman, Gerber, and Soderberg fatigue analysis to evaluate fatigue safety factors. Whether you’re designing shafts, gears, springs, or industrial machinery components, this easy-to-use calculator simplifies fatigue strength estimation, supports material selection, and helps improve mechanical design reliability.

Material properties

The material decides which estimation method is available. Steel correlations are not applied to other materials.

Stress unit
1 ksi = 6.894757 MPa. Switching converts the values already entered.
Minimum or certified value for your material and heat treatment.
Required for Soderberg analysis and the static yielding check; optional for Goodman and Gerber.

Surface, size, loading and environment

These choices set the Marin modification factors. Correlations are applied only within their documented range.

Loading type
Factor ke from Shigley Table 6-5 (Haugen and Wirsching), assuming an 8% standard deviation of the endurance strength.
Advanced settings: Marin factor overrides

Each factor uses its documented correlation (Auto) when one applies. Choose Custom to enter a value from your own data. When no correlation applies, a custom value is required and the modified endurance limit stays unavailable until you enter one. Allowed range: greater than 0 and at most 1.5.

Surface factor ka

Size factor kb

Load factor kc

Temperature factor kd

Reliability factor ke

Miscellaneous-effects factor kf

Default 1.0 assumes no additional reduction beyond the factors above. Use only with supporting data. Do not enter the fatigue stress-concentration factor Kf here; it belongs in step 4.

Cyclic stress analysis (optional)

Nominal stresses at the critical location, for a single loading type with proportional loading.

Tension positive, compression negative.
Multiplies both the alternating and mean nominal stresses (Shigley’s conventional approach). Use 1.0 for an unnotched section or if your stresses are already local.