Stribeck Curve Calculator
Feel the boundary → mixed → hydrodynamic transition by dragging the sliders
Compute the Hersey number Hn = η · U / P from viscosity, speed, and contact pressure, and watch the friction coefficient μ slide through the three lubrication regimes in real time. Tweaking composite roughness σ or the boundary value μ_bl reshapes the curve and moves the minimum.
Solid-on-solid asperity contact dominates. Wear is likely; boundary-additive films are the line of defence.
Solid-on-solid asperity contact dominates. Wear is likely; boundary-additive films are the line of defence.
Set conditions
Operating conditions (point)
Surface & contact (curve shape)
The λ correspondence is an approximate hint. For the rigorous λ, use the Lambda Ratio Calculator.
In the contact view, asperities (micro-roughness) of the upper and lower surfaces touch directly in boundary (red highlights) and are fully separated by the oil film (blue) in hydrodynamic.
One page with the inputs, results, equations, standards, and source URL.
Equations and standards
The Hersey number — viscosity, speed, and pressure collapsed onto the single axis of the Stribeck curve.
The share of load carried by asperity contact. Rougher surfaces push Hn_c right and widen the mixed regime.
Boundary and viscous contributions added; where they balance is the minimum of the curve.
Symbols and units
| Dynamic viscosity | Pa·s | |
| Sliding speed | m/s | |
| Contact pressure | Pa | |
| RMS surface roughness | µm | |
| Boundary friction coefficient | — | |
| Asperity load share | — | |
| Hersey number | m |
Valid range and limitations
- ·This is a semi-empirical teaching model. It reproduces the shape and the ordering of the regimes, but its absolute friction values are not meant to match a specific test.
- ·k_sigma, c_v, and p are tuned so the minimum sits in view for the default inputs; they are not fitted to measured data.
- ·Isothermal and steady state: no shear heating, running-in, or additive film formation over time.
- ·For a quantitative regime call, the lambda ratio calculator — film thickness against roughness — is the better instrument.
Reproduce in Excel
Hersey number
=A1*B1/C1A1 = eta in Pa·s, B1 = U in m/s, C1 = P in Pa.
Friction coefficient
=$D$1*(1/(1+(A2/$E$1)^$F$1))+$G$1*A2A2 = Hn, D1 = mu_bl, E1 = Hn_c, F1 = p, G1 = c_v.
Assumptions & Limitations
- This visualiser uses an educational semi-empirical model. Real friction coefficients depend strongly on contact geometry, materials, lubricant, temperature, and additive behaviour, and must ultimately be measured on a tribometer.
- The curve uses μ(Hn) = μ_bl · f_a(Hn) + c_v · Hn, where f_a is the asperity load-share fraction. The constants c_v, p, k_σ are tuned to produce visually clear regime transitions, not to reproduce a specific tribological test.
- Regime boundaries (f_a = 0.8 / 0.2) and the λ correspondence (λ ≈ 1 / 3) are approximate. Rigorous λ requires the EHL film-thickness calculation — see the Lambda Ratio Calculator.
- Hn = η · U / P uses η in Pa·s, U in m/s, and P in Pa. Real machines typically fall in the 10⁻¹² to 10⁻⁵ Hn range covered by the chart.
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