The Material Fatigue Life (S–N) Calculator is a practical engineering tool designed to estimate material fatigue life under cyclic loading conditions. Based on the Basquin stress-life equation, this calculator helps engineers determine the estimated number of cycles to failure using stress amplitude, fatigue strength coefficient, and fatigue strength exponent. It also provides S–N curve visualization to help users understand the relationship between cyclic stress and material durability. Ideal for mechanical engineers, material scientists, and product designers, the Material Fatigue Life (S–N) Calculator supports preliminary fatigue analysis, material evaluation, and component design optimization. Improve engineering efficiency and make informed decisions with accurate formula-based fatigue life estimates.

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Constant-amplitude loading. Use σف′ and b fitted to fatigue data for your material and condition.

Unit for every stress field and result. Changing it converts the values already entered. Calculations run internally in MPa.
A label for your report. It does not select any properties: the calculation uses only the coefficients you enter.
Required
Half of the stress range in one cycle, σa = (σmax − σmin)/2. It is the main driver of fatigue damage. Leave blank to derive it from σmax and σmin below.
Must be greater than zero. Optional only if σmax and σmin are both entered.
Intercept of the Basquin fit: the stress amplitude extrapolated to one reversal (2Nf = 1). Take it from fatigue test data or a documented reference curve for your material, heat treatment and surface condition.
Slope of the S–N line on log–log axes. Always negative; for metals it commonly lies between about −0.05 and −0.15. A smaller magnitude gives a flatter curve, so life is more sensitive to stress.
Optional: Stress Cycle
Highest stress in the cycle (tension positive). With σmin it gives the mean stress σm and stress ratio R, and a check on the entered σa.
Lowest stress in the cycle (compression negative). For fully reversed loading σmin = −σmax and R = −1.
Enter both values or leave both blank.
Optional: Reference and Target
Used only as a reference to check whether the peak stress is plausible for an S–N (high-cycle, nominally elastic) analysis. It does not change the calculated life.
Required design life. The calculator compares the predicted life with it and reports the stress utilization σa / σa,allow, where σa,allow is the Basquin stress amplitude at the target life.
Scientific notation is accepted, for example 1e6.