The formula for force is F = ma (Newton's Second Law of Motion). In this case, weight is the force, "F", the mass of the object is "m", and "a" equals the acceleration due to gravity. The new equation with the substituted variables is W = mg or the weight force is equal to the mass of the object times the acceleration due to gravity. If gravity were to remain the same while the mass of the object is doubled, the weight force is also doubled.