The relation between a ratio scale obtained by magnitude estimation and a category scale of the odour intensity of 1-butanol was studied, together with individual variations in the ratio scale. Series of solutions of butanol in water in small bottles were presented to a panel for judgement, half using the method of magnitude estimation, the other half a category scale. Plots were made of the category scale against the ratio scale, and the ratio scales of individual members of the panel were analysed. A power function exponent of 0.48 was found for the panel's ratio scale, with individual values ranging from 0.25 to 0.49. The category scale was curved relative to the ratio scale; variability of the magnitude estimates was approximately proportional to the magnitude estimates; and a small time-order error was found. Odour intensity exhibits the three tested characteristics of a prothetic continuum, and the variability of individual exponents was not as great as sometimes suggested.