The paper deals with diesel compressed air starting system calculation method based on the comparison between the compressed air efficient work and the work consumed by the air compression in the engine cylinder during the compression stroke. Approximate engine starting time duration depending on pressure in starting air receiver correlations were found, as well as compressed air consumption. The approximate correlations for calculating pressure drop in receivers depending on the receiver volume and the volume of air consumption at engine starting were given. The calculation of starting process using found out correlations was made for six cylinder slow speed engine as an example.