When you want to have milligrams you must to multiply grams by 1000, so 4.5 mg equals 0.0045 and you will not see it in your scale.

Is a tablespoon 15 or 20 ml?

Traditional definitions

In nutrition labeling in the US and the UK, a tablespoon is defined as 15 ml (0.51 US fl oz). A metric tablespoon is exactly equal to 15 ml (0.51 US fl oz).

Equal to 1/1,000 (one-thousandth) of a gram. About the mass of a small grain of sand (but sand grains can easily be 10 times more or less) or a typical grain of salt.

How many TSP is 10 mg?

10mL equals two teaspoons (2tsp). A tablespoon is three times bigger than a teaspoon and three teaspoons equal one tablespoon (1Tbsp or 1Tb). One tablespoon also equals 15mL.

Consider that 1 teaspoon of table salt, which is a combination of sodium and chloride, has 2,325 milligrams (mg) of sodium.