How to calculate growth rate: During balanced growth, the growth mimics a first order chemical reaction. dN/dt =kN N is the concentration of cells, t the time and k is the growth rate constant. The dimension of the specific growth rate k are reciprocal time, usually expressed as reciprocal hours, or hr^1. Integration of previous equation between the limits of 0 and t and N1 and N2 gives following equation. ln(N2/N1)=k(t2-t1) converting the previous equation to logarithmns to the base of 10, we get log10N2-log10N1 = k(t2-t1)/2.303 If one determines the number of bacterial CFUs present at various times and plots the log of that number, one gets a straight line (in log phase) From the slope of the line, we can calculate the specific growth rate k of the culture, which is the most encompassing parameter of how fast a particular bacterium growths in a particular media. For example, if a culture contains 10^3 cells at time t1 and 10^8 cells at t2 6 hours later, the specific growth rate k is k= (8-3) 2.303/6, which equals k=1.92 hr^-1 The dimension of the specific growth rate k are reciprocal time, usually expressed as reciprocal hours, or hr^1. How to calculate Generation or Doubling time: The rate of growth of a bacterial culture is oftern described by the time required for the number of cells to increase by a factor of 2, or the DOUBLING TIME or GENERATION TIME, g. The relationship between g and k can be established by using following equation. ln(N2/N1)=k(t2-t1) ln is the natural logs (log^e) N2 is cell number at t2 and N1 is the cell number at t1 k is the growth rate Since when N2 = 2N1, t2-t1 becomes equal to g Substituting values for t and N into the previous equation, we obtain following: g=ln2/k = 0.693k (reference: Physiology of the bacterial cell, a molecular approach by Frederick C. Neidhardt, John Ingraham and Moselio Schaechter)