how do i calculate my mass on earth
Those scales factor in the 9.81 m/s of gravity, they are measuring weight but giving a mass output. If the scales say 79.5 kg, then you technically 'weigh' 779 Newtons. Basically earth scales are onlyvalid on earth, as they mesure weight then divide by 9.81 to give the reasong in SI units.
Use the formula w = m x g to convert weight into mass. Weight is defined as the force of gravity on an object. Scientists put that sentence into an equation by writing w = m x g, or. w = mg. Since weight is a force, scientists also write the equation as F = mg.