The two basic methods for determining wood MC are the ovendrying method and the distillation method.  The ovendrying method is generally accepted for basic laboratory work and as a standard for calibrating other methods.  This method involves weighing a specimen before and after ovendrying to a constant weight at 103 C.  Because the quantities used for defining MC are measured directly, this method is the most precise.  However, it is physically impossible to remove all the hygroscopic water by heating without pyrolyzing the wood. Therefore, constant weight is defined as no further weight loss when a specimen is weighed to an accuracy of +/- 2 percent at 2-hour intervals.

If wood has been preservative-treated or impregnated with other chemicals, ovendrying moisture measurements may be inaccurate.  An impregnant that is volatile at oven temperatures will evaporate during ovendrying, and the resulting weight loss can be misinterpreted as due to evaporated water.  An impregnant that is nonvolatile will remain in the wood and so increase the apparent ovendry weight of the wood.  For treated wood, the distillation method may be more accurate than ovendrying for the determination of wood MC.  In the former method, water is removed from the wood specimen in a closed system, in which the water is collected and measured directly.  Any extraneous organic materials in the wood are dissolved out of the specimen by an organic solvent during the water extraction process.  The distillation method is also more accurate than then the ovendry method for some species that contain large amounts of volatile materials other than water.