Following an analogy between flow properties and field or transport properties, an equation which describes the porosity, P, dependence of the viscosity in porous sintered glasses is presented. Not only the pore volume fraction but also pore structure parameters, such as po re shape a nd orientation, a re considered in the calculation and the equation is valid for the whole porosity range. For low porosities (P less than or equal to 0.10) the approach coincides with the prediction of Mackenzie for spherical pores with a precision of 1%. The calculated values are in good agreement with experimental data on porous glasses available from the literature, if appropriate pore geometry is assumed at the different porosity levels.