Liquid foams are obtained by independently fixing foaming solution and gas flows through a coarse porous structure. Precise measurements of these flows immediately give the gas-volume fractions of the foams; real-time diffractometry gives their initial bubble-size distributions and these are found to be lognormal. — The proposed methods provide reproducible foams and are sensitive. They will be useful to test the interbubble gas transfer theory and to grade surfactants according to their ability to form persistent foams.