Converting between nanograms per milliliter and picograms per milliliter is quite simple. Because both units are part of the International System of Units (SI), the conversion can be accomplished by simply moving a decimal point. Of the two units, the nanogram is larger than the picogram; in fact, the nanogram is 1,000 times larger. This means, to convert from nanogram to picogram, simply move the decimal to the right three places. To convert from picogram to nanogram, move the decimal to the left three places.