Significance Cell signaling involves interpreting information from the environment and implementing the appropriate regulatory control. The ppGpp signaling system is known to exert a fundamental control in bacteria, coordinating ribosome synthesis with the rate of cellular growth, but how this system can sense the cellular growth rate in different environments is unclear. Here we establish a striking linear relation between ppGpp level and the reciprocal of the translation elongation rate (ER) and show how bacteria can process complex nutritional information by monitoring this rate and using it to control ribosome synthesis. Importantly, the sensing of ER through ppGpp quantitatively and mechanistically explains bacterial growth laws which robustly relate the ribosome content and translation ERs to the growth rate.