This calculator will help you computes the different properties of a gaussian beam.
The formulas that will be used are as followed:
Laser Wavelength $\lambda$, Waist radius $w_0$, Distance to waist radius $z$
Far field divergence angle $\theta$, Rayleigh length $Z_R$, Spot diameter at Z $d(z)$, Radius of wavefront curvature R(z)