What does concrete grade M25 mean?

M25 concrete means the concrete has a characteristic compressive strength of 25 MPa (N/mm2) at 28 days when tested on standard 150mm cube specimens. 'M' stands for Mix, and the number represents the strength in MPa. Common grades include M15, M20, M25 (general construction), M30, M35 (structural), and M40+ (high-strength applications). Higher grades require lower water-cement ratios and often include admixtures or supplementary materials.