if it's a paste, then just use the screw-cap to point to your weight. If you weigh 250, then point it to 250 and then plunge out that amount If you weight 125, then point to it and then plunge out that amount. you may want to do a "half turn" to split the difference. It's basically a small teaspoon. You can't mess it up too much. It's forgiving. But why even use it as a prophylactic? Everyone will get Covid eventually. Just get it first and then use it. If you get sick, celebrate your body learning how to deal with it like a parent celebrates their kids getting over chicken pox. edit: sorry, i wasn't paying attention. the amount I suggest is if you are trying to get rid of worms. if you are using it as a prophylactic then you do your own measurements.