There is no single chemical formula for stainless steel. Stainless steel is an alloy, meaning it's a mixture of different metals. The most common type is austenitic stainless steel, which is a mixture of:

* Iron (Fe) - the primary component

* Chromium (Cr) - typically 10.5% or more, which gives it its corrosion resistance

* Nickel (Ni) - typically 8% or more, which improves its ductility and strength

* Other elements - such as manganese, molybdenum, nitrogen, and carbon, which can be added in smaller amounts to modify its properties.

The specific proportions of these elements can vary depending on the desired properties of the steel.

Therefore, there is no single formula, but rather a range of possible compositions. For example, some common grades of stainless steel include:

* 304: 18% Cr, 8% Ni

* 316: 16% Cr, 10% Ni, 2% Mo

* 430: 17% Cr

It's important to note that the chemical formula is not the only factor determining the properties of stainless steel. Factors like heat treatment and processing also play a significant role.