Abstract <p>In this study we quantify the uncertainty relative to a novel Lagrangian tracking technique to measure the complete solid-body rotation rate of anisotropic micro-plastic fibers. By exploiting their geometry—specifically, their elongation and curvature for tumbling and spinning rate measurements, respectively—we address a gap in the literature regarding the tracking of fibers’ unique orientation along their trajectories. The impact of fiber geometry and imaging parameters on the accuracy of the solid-body rotation rates measurements is investigated. The influence of spatial and temporal resolution on the measurement uncertainty is assessed on synthetic data. Experimental results obtained in a channel flow demonstrate the method’s potential to accurately detect rotations of fibers with lengths approaching the Kolmogorov scale.</p> Graphical abstract <p></p>