The breathing act is usually quite noticeable in most vertebrates; hence, the measurement of breathing frequency (f) rarely poses a serious problem. Differently, the quantitative assessment of tidal volume (VT) (from which air ventilation, V˙E=fVT, is computed) can be a major challenge. This article reviews the most common experimental approaches to quantify VT in adult or young vertebrates of small body size. In these animals, techniques commonly used in adult humans are unsuitable. Furthermore, physiologically meaningful data necessitate techniques with minimal disturbance to the subject under investigation. During the last fifty years numerous and ingenious approaches have been developed and refined. Although none of them can be considered ideal or totally error-free, for specific tasks and/or species there is an optimal approach to measure tidal volume.