The distinction between mass and weight should always be kept in mind. While mass is a property of an object itself, weight is the force it exerts, which is dependent on e.g. the strength of local gravity. The mass of an object is identical on Earth and on the moon, while the weight is different.
For reference, the mass of a large elephant is 10,000 kg, and of a mouse is around 20 g. A grain of sand may have a mass of 10 µg to 10 mg, depending on its size.