Hi.
It’s all about volume. Really the weight doesn’t matter so do 485ml of rice so just measure it out in a Pyrex jug, at a smudge below 500ml. Stick it in an old tight leg and hey presto, repeat for other boob 😉 if you are neat with your knots use the knot to locate it over your nipple.
Also when it’s tied post it down so it’s around 12/13cm wide then that will be around the sort of size of the implant. From my experience I recommend you put them into a pull on sports bra one that has quite a high front, the sort you can just wear as a crop top. They are good for helping to smooth it out and give a general outline, then west as much as possible heck go try some
New clothes on whilst wearing them helped me to get more of an idea of size