The ratio of steel to concrete is 100:130 for 1 cubic meter. The ratio means that for every 130 kg of concrete, 100 kg of steel is needed to support the structure. This is a rule of thumb in civil engineering that must be observed at all times, as failure to observe it renders buildings prone to ductility and cracking.
The ratio is a fundamental agreement reached by professional engineering bodies across the world. However, some buildings may use different ratios depending on the design, architecture and the purposes for which they are being built. For example, a building meant to house a car park should naturally be built stronger than one meant for offices. In this case, the ratio of steel to concrete may be virtually equal.
In addition, the quality of steel used matters a lot. Other factors that may determine the strength of concrete are the age of concrete, temperature, humidity, curing of concrete and other raw materials used. The shape, texture, size and strength of aggregates, for example, determine how strong a structure will be. Similarly, the presence of salts such as sulphates and chlorides, clay and salt reduces strength of concrete. In addition, the water-to-cement ratio and coarse-to-fine aggregate ratio of building materials also affect the strength of a structure.