This paper deals with the use of Whispering Gallery Modes to measure the six components of an homogeneous strain tensor within a sphere undergoing a uniform strain field. The device is a silica sphere in which six WGMs resonate, describing six circles positioned on the sphere’s surface in planes perpendicular to the normals of a dodecahedron. The direct model relating the strain to the resonant wavelength variation is established for one circle and then linearised in accordance with the intended application, i.e. the realisation of a sensor. The expressions are then generalised to six circles and inverse system computed to obtain an expression for the six components of the strain field as a function of six wavelength shifts of WGMs. Finally, the theoretical performances of the sensor are assessed. The study shows that using a conventional 1 pm resolution detector, the uncertainty on the strain components is, after correction of systematic errors, equal to 2 με .