A relatively large error due to the meniscus volume in measuring low pressures with a McLeod gauge is described. The accurate volumes of mercury meniscus for capillaries have been calculated from the Laplace's differential equation with a digital computer. The results have been tabulated as a function of meniscus height for radii of 0.3 to 1.0 mm. Some correction methods in the pressure measurements with the aid of this table are discussed. It has been confirmed that a formula obtained by the spherical surface approximation easily gives the meniscus volume for capillaries of 2 mm diameter or less within 2 per cent in error.