Grouting of underground constructions is important to decrease water inflow into constructions. It is therefore important to use grout with good penetration ability to achieve this goal. The purpose of this paper is to show issues connected to measuring of the penetration ability of cement-based grouts in the field with a filter pump and penetrability meter and show the need for improvement or use of some other method. Three main reasons which contribute to a different estimated critical aperture with these two methods are: different maximum test volume in regression analysis of measured data, limited maximum test volume in the filter pump, and different test pressure. Test volume should be related to volume of designed grout spread in the critical aperture and test pressure should be related to grout spread velocity in the field.