Conductive diamond films are essential for electronic applications of diamond but there is still a poor understanding of the effects that growth conditions, grain size and film thickness have on the ultimate conductivity of the film. One of the unique advantages of hot filament diamond is the ability to grow both MCD and NCD films to moderate thicknesses over large areas with little or no change in morphological characteristics such as grain size. In addition the grain size of the film can be altered without the necessity of adding additional gases to the process or unduly increasing the carbon to hydrogen ratio. This gives us an opportunity to investigate electrical conductivity as a function of grain size and thickness within a simple methane, hydrogen, and boron chemical environment over areas which are large enough to support significant production levels of MEMS and other diamond based electronics. In this study the boron source was selected to be trimethyl boron gas to avoid any source of oxygen which could alter the growth conditions and to guarantee that any byproducts of the dopant would be primarily methyl based. The films were grown to various thicknesses up to 5 micrometers and grain sizes from NCD to full MCD at all thicknesses. This paper explores the effects of both grain size and film thickness on the electrical conductivity of the film as well as the absolute doping levels within the film.