Exa 1018
Peta 1015
Tera 1012
Giga 109
Mega 106
Kilo 103
Hecto 102
Deka 10
Deci 10-1
Centi 10-2
Milli 10-3
Micro 10-6
Nano 10-9
Pico 10-12
Femto 10-15
Atto 10-18

So: 1000 grams = 1 X 103 = 1000 or 1 kilo

1000 kilos = 1 metric tonne = 1 X 106 = megagram

1 million tonnes = 1 X 109 = 1,000,000,000 grams = 1 gigagram

1 petagram = 1 X 1015 = 1,000,000,000,000,000 = 1 trillion grams = 1 billion metric tonnes