Is that round to 4 grams?

That is correct. It was an oversight on my behalf.

I suck at metric, but I am trying to use it, especially in the water chemistry/adjustment side of things....

Learning to be comfortable with the metric system is like learning a foreign language. The problem at first is that one wants to think in one's native language and translate. What happens over time is that one learns to think in the foreign language, and that is what happens with the metric system. The metric system is superior to our modified English unit of measurement system. It's a base-10 system of measurements that matches our base-10 number system.

I will give you an example; namely, weight by volume (w/v) and weight by weight (w/w) solutions. While a milliliter of water weighs one gram, a U.S. fluid ounce of water weighs 1.0432 dry ounces. A 1L (1000ml) solution that contains 100 grams of extract is a 100 / 1000 * 100 = 10% w/v solution. A 1 U.S. quart 10% w/v solution contains 3.2 * 1.0432 = 3.34 dry ounces of extract. Which solution is easier to calculate in one's head?

By the way, a 10% w/v solution has a specific gravity of 1.040, which why one sees it along with 5% w/v (1.020) solutions used so frequently when preparing laboratory media. A 10% w/v solution is a 10 Degree Plato solution when the solute is water because 1ml of water weighs 1 gram, and Degrees Plato is a weight by weight system. A beautiful thing about working with weight by weight when the solute is water is that one can determine the S.G. of a solution at 16C/60F by knowing the weight of the solution and the weight of the extract mixed into solution. No hydrometer is required.

S.G. = 259 / (259 - (extract_weight / solution_weight * 100))

One should use 260 instead 259 for gravities of 17.5 Plato and above.