Conversions for a Metric Concentration Deck

Design a set of 20 cards: The size, shape, and design on the backs of the cards is up to you, with one condition: when you lay out the cards, they must tile the plane (fit together perfectly without gaps or overlaps).

Write on the faces of the cards:

 1 m 1000 mm 1 m 100 cm 1 km 1000 m 1 km 1 thousand m 1 gram 1000 milligrams 1 g 1000 mg 1 kilogram 1000 grams 1 kg 1000 g 1 megagram 1,000,000 g 1 Mg 1000 kg

Use your 20-card deck to play a game of Metric Concentration:

1. Shuffle the deck and lay out the cards face down.
2. Each player turns 2 cards face up. If the cards match, the player collects them; if not, they are turned face down. Then it's the next player's turn.
3. How can you be sure that two cards match? Check the original list above. All cards in the same row match. For instance, any two of 1 m, 1000 mm, 1 m, or 100 cm are a match. Similarly, any two of 1 Mg, 1 megagram, 1,000,000 g or 1000 kg would be a match.
4. Continue until all cards have been collected. The player with the most cards wins.