The state parameter is a quantitative measure of the state of a sand that combines the effects of void ratio and effective stress in a unique way for each sand. Application of the state parameter concept in practice requires the ability to measure the state parameter in situ. This Paper examines the interpretation of the cone penetration test in sand in terms of the state parameter concept. Existing data obtained from calibration chamber tests are reinterpreted to provide the relationship of cone tip resistance to state parameter. To compare data from different test programmes, data must be adjusted for chamber boundary effects. It is concluded that cone resistance provides a good measure of the state parameter. A companion paper describes the generalized measurement of state in different sands using the cone penetration test. Le parametre d'etat est une mesure quantitative de l'etat d'un sable qui combine les effets de l'indice des vides et de la contrainte effective de facon unique pour chaque sable. Da...