#### Answer

My suitcase weighs 20 kg.

#### Work Step by Step

My suitcase weighs 20 kg.
If the suitcase weighs 20 g or 20 mg, these weights are both much less than 1 kg, and an estimate of 1 kg for a suitcase seems too light. Even a suitcase that is packed with a few basic items would normally weigh several kilograms.
Therefore, the most reasonable metric unit for the weight of the suitcase is the kilogram.