What is the concentration of ATP in an average cell?
Answer

This article covers the energy charge and ATP concentrations of an array of muscle cells from many different organisms. Since many factors come into play (amount of glucose available, rate and regulation of glycolysis and cellular respiration, use of energy in metabolism, etc.) it is expected for the ATP concentration within the cell to vary significantly. The ATP concentrations reported span from approximately 1 to 10 mM.



References

 - Beis, I, and E A Newsholme. “The Contents of Adenine Nucleotides, Phosphagens and Some Glycolytic Intermediates in Resting Muscles from Vertebrates and Invertebrates.” Biochemical Journal 152, no. 1 (October 1975): 23–32.