The high‐temperature ash levels of some typical U. S. bituminous coals can be rapidly estimated with a standard error (absolute) of 1.7% ash from simple linear correlations between % Si and % ash. Si contents may be rapidly determine by Fast Neutron Activation Analysis (FNAA), X‐Ray Flourescence (XRF), or Slurry‐Injection Atomic Absorption Spectrometry (SIAAS) methods requiring little more sample preparation other than a brief grinding and weighing. These three instrumental methods showed roughly equivalent correlations. In contrast to earlier reports, logarithmic plots do not produce improved estimates. Also, correlations do not seem to be significantly improved by selecting coals within one rank or from one geographical area. The slurry‐injection atomic absorption method does not require significant modifications of existing commercial AA instruments. The conventional method for determining ash content of coal, though simple and accurate, requires a considerable amount of time in the laboratory. Ash content of coals is an important parameter related to their eventual use as fuels, as feedstocks in liquefaction and gasification processes, and in metallurgical processes.