We investigate experimentally the relationship between the pitch and the elastic constants of a transient planar state in cholesteric liquid crystals. The pitch of the transient planar state is measured by the optical reflection technique. The twist and bend elastic constants of cholesteric materials are determined from the measured values of the threshold voltages for the transitions between a focal-conic state and a homeotropic state. By comparing these values, we experimentally confirm the relationship for the pitch of a transient planar state; P-transient = (K-33/K-22)P-0, which has been suggested theoretically.