N = N₀ × 2^(t / g)
During the log phase, bacteria divide by binary fission at a constant rate. The population doubles every generation time (g): N = N₀ × 2^(t/g). E. coli has g ≈ 20 min under optimal conditions — starting from 1 cell, you'd have over 10²¹ cells in 24 hours (if resources were unlimited). The growth rate constant k = ln(2)/g. Real bacterial growth follows 4 phases: lag (adaptation), log/exponential (rapid growth), stationary (resources depleted, death = growth), and death. Factors affecting g: temperature, nutrients, pH, and oxygen. Understanding bacterial growth is essential for food safety (time in the danger zone 4-60°C), clinical microbiology, and industrial fermentation.