Antibiotics are central in modern medicine, and the threat of antimicrobial resistance makes it important that we use them as effectively as possible. Yet there are surprising gaps in our understanding of how antibiotics work in growing bacterial cells. Antibiotics that target the bacterial cell wall account for the majority of clinical usage. Building on the results of simple growth experiments on different media and using different cell wall targeting antibiotics, we have developed a mathematical model for the interplay between bacterial growth and the action of cell wall targeting antibiotics. Our model suggests that the balance between bacterial surface area and volume growth may play a crucial role.