The stripping ratio is a number that represents the amount of overburden that must be excavated to mine an amount of ore (or coal). The stripping ratio is very important when determining the economic feasibility of a particular orebody, or the most economic mining method for a particular orebody. 

In order to calculate the stripping ratio you divide the overburden removed by the ore (or coal) recovered. For example, a 4:1 stripping ratio means for every 4 units of overburden, 1 unit of ore can be recovered. Common units used to determine the stripping ratio are volume overburden:mass ore (e.g., yd3/ton); or, for flat tabular deposits only, thickness overburden:thickness of deposit is used (e.g., ft/ft or m/m as shown below). When reviewing stripping ratios, it is important to understand the units used to calculate the ratio, since different units may yield very different ratios.

For very high stripping ratios, it may not be economic to use surface mining methods, underground mining may be considered.

Figure: As shown, 80 meters of overburden must be removed to mine the 50 meters of coal, producing a stripping ratio of 1.6.