Properties of 1,4-trans-poly(isoprene) at ambient conditions are determined by simulations on two length scales based on two different models: a fully atomistic and a mesoscopic one. The models are linked via a mapping scheme such that one mesoscopic bead represents one chemical repeat unit. Melts as well as solutions of several chain lengths are investigated and mapped individually to the mesoscale. The resulting models are compared to each other. The meso-scale models could be simulated over a large variety of chain lengths and time scales relevant for experimental comparison. Concerning static properties, we determine the persistence length and the scaling behavior of the radius of gyration. The latter is compared to experiments, and the agreement is satisfactory. Furthermore, we find deviations from Rouse dynamics at all chain lengths at ambient conditions.