In real polymer systems both intra-chain and inter-chain components contribute to charge transport, though extent of the contribution depends on the conformation of the chains. With the assumptions that the characteristic time-scale of inter-chain hopping (𝑡 𝑖𝑛𝑡𝑒𝑟 ) is much larger than that of intra-chain hopping (𝑡 𝑖𝑛𝑡𝑟𝑎 ) (𝑡 𝑖𝑛𝑡𝑒𝑟 ≫ 𝑡 𝑖𝑛𝑡𝑟𝑎 ) and the displacement due to significantly infrequent inter-chain jumps contributes very little to the final charge-carrier displacement from the initial position, the charge diffusion coefficient in 3D can be roughly defined as 𝐷 3𝐷 = 〈𝑅 2 (𝑡 𝑖𝑛𝑡𝑒𝑟 )〉/6𝑡 𝑖𝑛𝑡𝑒𝑟 , where 〈𝑅 2 (𝑡 𝑖𝑛𝑡𝑒𝑟 )〉 is the mean squared displacement of the charge in the characteristic inter-chain charge-carrier hopping time. For sufficiently rigid polymers where the charge primarily moves along the chain backbone, 〈𝑅 2 (𝑡)〉 is related to the diffusion coefficient in 1D (𝐷 1𝐷 ) via 〈𝑅 2 (𝑡 𝑖𝑛𝑡𝑒𝑟 )〉 = 2𝐷 1𝐷 𝑡 𝑖𝑛𝑡𝑒𝑟 , since the charge motion is similar to the random walk problem in 1D. This leads to the final conclusion that 𝐷 3𝐷 = 𝐷 1𝐷 /3 and in turn, through Einstein relation, the average chargecarrier mobility in bulk is 1/3 of the average intra-chain mobility.