An empirical formula that predicts the spatial resolution of a thermal neutron detector comprising of wavelength-shifting (WLS) fibre arrays coupled with a ZnS/(LiF)-Li-6 scintillator screen was derived based on experimental results. The spatial resolutions of the test detectors were measured separately in order to evaluate the contributions due to light spreading within the scintillator and the WLS fibres layers. The empirical formula involved the scintillator thickness and the diameter of the WLS fibres. The results calculated using the derived formula faithfully reproduced the results obtained experimentally with the test detectors, demonstrating the feasibility of using the formula when designing the neutron detecting head for this type of detector.