Accurate individual norms are required for blood volume measurement to be useful in a clinical setting. The primary physiological determinant of normal blood volume is body composition. Norms have been developed based on weight and body surface area, but these have systematic errors arising from variations in body composition or body size. The only norm that specifically estimates body composition uses deviation from ideal weight. A clinically useful norm must also include a normal range that is sufficiently sensitive and specific. The ultimate test of a norm's effectiveness is how it relates to known physiological factors or outcomes in a clinical or research setting. When tested in relation to outcome results from previously published clinical studies, norms utilizing deviation from ideal weight provide the most accurate categorization of blood volume status.