A Briggs and Stratton lawn mower typically takes between 1.5 and 2 quarts of oil. The amount of oil needed will depend on the model of the lawn mower as well as the size of the engine. Checking the owner's manual for your specific model will give you the most accurate information. Overfilling the engine with oil can cause damage, so it is important to be careful not to add too much. If you are unsure how much oil to add, it is always better to err on the side of caution and add a little less rather than risk damaging your lawn mower.