A manual inflatable device intended to be inserted intraoperatively into a tissue pocket surgically-created for the acceptance of a breast augmentation implant, to provide a volume measurement for the appropriate selection of the implant; it is not designed for tissue expansion or to create the tissue pocket. It is a balloon-like device connected to a manually-powered air pump used to expand the device; devices associated with the sizer introduction may be packaged with the sizer. This is a single-use device.