Dimensions and proportions of the human body in sitting posture are ergonomical important, because our body is supported by seats every day from early infancy to old age. Based on a stratified sample of 42,000 persons, aged from birth to 70 years, and living in German cities, town and villages, reference values of trunk-cephalic height, trunk length, physiognomic leg length, and additive arm length are presented in relation to sex and age. The proportions of these basic measurements to height are given additionally as well as the intermembral-index (100 x additive arm length/physiognomic leg length) and the scelic index (100 x physiognomic leg length/trunk length). The different average velocity of the bodily development among both sexes is analysed and discussed. The second part of the article is dedicated to the important question of the variability of measurements in sitting posture during adulthood. Percentiles of trunk-cephalic height, trunk length, depth of the lower trunk, maximum sitting breadth, vertical thigh diameter, lower leg and foot length, backrest-heel distance, and additive arm length are presented by sex, age and type of body shape.