Measurements of charm mixing parameters from the decay-time-dependent ratio of D0→K+π− to D0→K−π+ rates and the charge-conjugate ratio are reported. The analysis uses data, corresponding to 3 fb−1 of integrated luminosity, from proton-proton collisions at 7 and 8 TeV center-of-mass energies recorded by the LHCb experiment. In the limit of charge-parity (CP) symmetry, the mixing parameters are determined to be x′2=(5.5±4.9)×10−5, y′=(4.8±1.0)×10−3, and RD=(3.568±0.066)×10−3. Allowing for CP violation, the mixing parameters are determined separately for D0 and D¯0 mesons yielding AD=(−0.7±1.9) %, for the direct CP-violating asymmetry, and 0.75<|q/p|<1.24 at the 68.3 % confidence level, where q and p are parameters that describe the mass eigenstates of the neutral charm mesons in terms of the flavor eigenstates. This is the most precise determination of these parameters from a single experiment and shows no evidence for CP violation.