ASTM D4868 Estimation of Net and Gross Heat of Combustion of Burner and Diesel Fuels
3. Summary of Test Method
3.1 The density and sulfur, water, and ash content of the sample are determined by experimental test methods. The heat of combustion is calculated using the values obtained by these test methods based on reported correlations.

4. Significance and Use
4.1 This test method is intended for use in cases where an experimental determination of heat of combustion is not available and cannot be made conveniently, and where an estimate is considered satisfactory. It is not intended as a substitute for experimental measurement of heat of combustion.