The investigation of multiphase flows asks for the volume of individual bubbles. Natural asymmetries and oscillations of the bubble shape suggest 3D shape analysis which entails considerable effort. Here, 2D image analysis is used instead. Three examples show in order of increasing complexity that 2D digital images allow the evaluation of the bubble volume after a preliminary calibration. The latter serves to normalize the image processing with respect to bubble images of exactly known volume. Even with strong shape oscillations, where statistical means become necessary, the correct volume is obtained.