Please check my doses

So, I'm trying to figure out doses for myself. I want to give three boys Advil the concentration is 50 mg/1.25 ml

So I took 50/1.25 = 40mg/ml

Hank 672 grams
0.672 divided by 40 = 0.0168 So he should get .02ml

Tucker 494 grams
0.494 divided by 40 = 0.01235 So he should get .01ml

Wally 561 grams
0.561 divided by 40 = 0.014025 So he should get .01ml

That seems like such a small dose so I don't think I'm doing this correctly. I cannot make any sense out of what the rat guide says.

Well your first calculation is correct! That's how you find out the strength of the medicine.

Next, you want the dosage. So ya go to ratguide and figure that out.
http://ratguide.com/meds/nsaids/ibuprofen.php
Let's go with 10mg/kg.

You are correct with your kg conversions, grams are converted by putting a decimal before the first number.

So, now we figure out how many mgs to give a rat that is say 672 grams instead of 1 kg (since we know a 1 kg rat would get 10mg of medicine.)

You do this by cross multiplying. You take what you know and put it across from what you want to know.

So,
10 mg / 1 kg = x mg / .672 kg
And multiply across.
10 times .672 = 6.72
And then 1 kg times x mg just becomes "x" or our answer, to signify the missing variable is 6.72

So now we know that Hank needs 6.72 mg and we know that in each ml of your liquid, there is 40 mg of medicine.

So,
6.72 / 40 = .168 or round up to .17 cc

I hope that helps a bit, it's rather hard to explain with text.

Ps Tuckers dose will be .13 cc and Wallys dose will be .14 cc

Thanks, was actually just able to help someone else out with this