A new estimate of Jupiter's planetary magnetic field is obtained from the Voyager 1 observations of the Jovian magnetosphere. An explicit model for the magnetodisc current system is combined with spherical harmonic model of the planetary field with both sets of parameters determined simulataneously by using a nonlinear generalized inverse methodology. The resulting model fits the observations extremely well throughout the analysis interval (r>20 Rj). The Jovian internal field model obtained from the Voyager 1 data is very similar to the octupole Pioneer 11 models. The best fitting magnetodisc lies in the centrifugal equator, 2/3 of the way between the rotational and magnetic equators, as is appropriate for centrifugal loading of the magnetosphere by a cold plasma. No statistically significant evidence is found for secular change of the equivalent dipole estimated from Pioneer 11 (1974.9) and Voyager 1 (1979.2) data.