Magnetic field (up to 8T) and temperature (10-300K) dependence of size of Zn doped magnetite samples Fe_3-xZn_xO₄(x=0.008, 0.022, i.e. falling within first and second order Verwey transition regime) were measured by the strain gauge method. Both samples experienced shrinking on cooling through the Verwey transition along monoclinic c axis, while the strong expansion was found for the 1^storder sample in the a-b direction, unlike in the 2^ndorder sample. Magnetostriction of both samples is very small and limited to low fields only, concomitant with magnetization process. However, field application perpendicular to c axis and at T slightly below the Verwey transition temperature TV results in a large change of dimensions, coinciding with the axis switching process.