Studies have shown that pyrolysis method and temperature are the key factors influencing biochar chemical and physical properties; however, information on the nature of biochar feedstocks is more accessible to consumers, making feedstock a better measure for selecting biochars. This study characterizes physical and chemical properties of commercially available biochars and investigates trends in biochar properties related to feedstock material to develop guidelines for biochar use. Twelve biochars were analyzed for physical and chemical properties. Compiled data from this study and from the literature (n = 85) were used to investigate trends in biochar characteristics related to feedstock. Analysis of compiled data reveals that despite clear differences in biochar properties from feedstocks of algae, grass, manure, nutshells, pomace, and wood (hard- and softwoods), characteristic generalizations can be made. Feedstock was a better predictor of biochar ash content and C/N ratio, but surface area was also temperature dependent for wood-derived biochar. Significant differences in ash content (grass and manure > wood) and C/N ratio (softwoods > grass and manure) enabled the first presentation of guidelines for biochar use based on feedstock material.