The purpose of this study was to examine a variety of mathematical volume formulae and their respective validity in establishing limb volume in monitoring and evaluation of treatment for lymphoedema. Using a random sample of treatment records from the Day Ward, Worthing Hospital, it is shown that the formula most commonly used at present, that for a cylinder, produces imprecise volume data. A simplified formula derived from the formula for a frustum is tested, and is found to produce more accurate data. The paper proposes that the frustum formula is more appropriate in establishing limb volume, and should be adopted by practitioners.