There can be no equivalence.
A milligram is a measure of mass. A millilitre is a measure of volume. The two measure different things and,according to basic principles of dimensional analysis, conversion from one to the other is not valid.
If you are not convinced, consider a millilitre of air. How many milligrams? Next consider a millilitre of water. How many milligrams?
The masses of equal volumes of the two substances will clearly be very different. So there is no direct conversion between mass and volume: you need to know the density of the substance to enable you to carry out the conversion.
Some people still believe that there is a conversion in relation to pure water but that is only approximately true. Until 1964 (nearly 50 year ago!) a litre was defined as the volume of one kilogram of pure water at 4 degrees Celsius and at a pressure of 760 millimetres of Mercury. With that definition a conversion would have been possible - but only for pure water and only under those conditions. In any case that definition of a litre was abandoned in favour of 1 litre =1000 cubic centimetres. As a result, the density of water at one atmospheric pressure is always less than 1. Its maximum value. at 4 deg C, is 0.999 972 g/cm3, not 1.
These are two different units of measure (volume and weight/mass) that do not convert to one another.
200mls?
It depends on the density of the milk which, in turn, will depend on the amount of cream that it contains. Or, if you get your milk from a dodgy supplier, the amount of water!
4-5 800mg
There are 1 ml in 1 mg, so 800 mg would be equal to 800 ml.
800mg
apples and oranges. they work in different ways.
No
Well it depends on what you are measuring! One is volume the other is weight.
800mg
1900 ml
That is 3.75 ml.