The aim was to make bioimpedance spectroscopy (BIS) quantitative for assessment of lymphoedema. Apparent resistivity coefficients were determined for the intra- and extracellular water of arms in a control cohort of women (n = 66). These coefficients were used to predict water volumes in the arms of women with lymphoedema (n = 23) and a separate control group without lymphoedema (n = 13) and to compare these with total arm size measured by perometry. Total arm volume was highly correlated (r = 0.80-0.90) with arm fluid volumes predicted by BIS and the proportional increase in arm size predicted by BIS was not significantly different to that measured by perometry. BIS predicted that the increased volume in the women with lymphoedema was predominantly (60%) due to increase in extracellular fluid. BIS is capable of quantifying the volume increase in limb size seen in lymphoedema.