Feedback control of metal strip rolling processes requires inline-capable, fast and robust thickness gauges. An optical thickness gauge is developed which measures the distance to the top and bottom of the strip with two optical sensors. They combine triangulation and multi-wavelength interferometry for a robust absolute high-resolution range measurement. Sinusoidal modulation interferometry is used to realize a very compact Fizeau-type multi-wavelength interferometer. The performance of the thickness gauge is studied in the laboratory under dynamic conditions that are close to production environment. The expanded measurement uncertainty of 0.48 μm of the system is thereby consistent with the observed deviation of the measurement values from a tactile reference sensor