Thumb rules play a most crucial role while taking quick decisions on site. Thumb rules enable you to calculate the solution using a simple mathematical formula and make smart decisions whenever needed. Remember, thumb rules never give accurate results, but you can use them for approximate results. There are many thumb rules which we apply in construction The Thumb rule is an approximate & comparing method. In thumb rules, The units are not the same when we compare to get the results. So never consider units while performing the thumb rule.