Abstract: An apparatus and method for mixing fuel and oil, to achieve a desired mixture ratio, includes calculating a required number of fuel units, to be mixed with a predetermined volume of oil, for achieving the desired mixture ratio, as a function of calculation terms including the desired mixture ratio and an arbitrarily selected correlation number correlating the predetermined volume of oil to the desired mixture ratio. The required number of fuel units is thus calculated without the use of a calculation term equaling the predetermined volume of oil, thereby facilitating accurate mixing of even custom mixture ratios with simple calculations that can be done mentally.