An attogram is a unit of measure equal to 10 ^ -18 grams.
Some examples are radiogram, telegram, attogram, diagram, pentagram.
10-18 is atto- So 10-18 metre is 1 attometre, that is 10-18 m = 1 am; 10-18 gram is 1 attogram, that is 10-18 g = 1 ag; etc.
Yes. Grams use the same standard unit conventions as meters, bytes, liters, and anything else that uses the Greek naming conventions for unit sizes. So the next units smaller than milligrams would be: 1 microgram = 0.000 001 grams 1 nanogram = 0.000 000 001 grams 1 picogram = 0.000 000 000 001 grams 1 femtogram = 0.000 000 000 000 001 grams 1 attogram = 0.000 000 000 000 000 001 grams 1 zeptogram = 0.000 000 000 000 000 000 001 grams 1 yoctogram = 0.000 000 000 000 000 000 000 001 grams