Power-frequency (50/60 Hz) magnetic fields produced by electric blankets are estimated from data on blanket design using a three-dimensional computer model. Maximum, minimum, and volume-average fields within human forms are presented as a function of blanket type and a number of geometric factors including body size, body-blanket separation, and lateral body position. When blankets are heating, typical flux densities range from a few tenths of microtesla (microT) on the side of the body farthest from the blanket up to a few tens of microtesla on the side closest to the blanket. Superposition results in local minima within the body that approach zero field intensity. Across the blanket-using population, flux densities averaged over the whole body range from 1.5-3.3 microT with typical values of 2.2 microT.