We present the adaptive optics simulations we have performed to dimension the Gravity adaptive optics wavefront sensor. We first computed the optimal WFS bandpass, depending on the sampling frequency, detector readout noise and reference source colour/temperature. We then performed adaptive optics simulations with the YAO simulation tool for different WFS parameters (number of subpupils, number of pixels per subpupil, loop frequency, reference source magnitude, etc). Results demonstrate that the Gravity adaptive optics top-level requirements can be fulfilled with a 9×9 subaperture Shack-Hartmann with 4 pixels per subaperture using an H+K filter, a larger filter being recommended for sources bluer than 770 K reference source of the Galactic Centre.