Free calculator
Drops to grams calculator
A drop is not a unit: its size depends on the material, the dropper and the hand. So this does not convert drops for you. It turns a weighing of your own drops into a figure you can use for that material and that dropper, and nothing else.
The sum, in words
Count a number of drops onto the balance, note what they weigh, and divide the weight by the count. That is what one drop of that material weighs from that dropper. Multiply it by the drops in an old note and you have the note in grams.
Twenty drops weighing 0.9 g is 0.045 g a drop. A note that says twelve drops is then 12 multiplied by 0.045, which is 0.54 g. Write down 0.54 g, and from then on weigh it.
Why count twenty drops rather than one
One drop of most materials weighs a few hundredths of a gram, which on an ordinary two-decimal balance is inside the balance's own uncertainty. The display shows a number and the number means very little.
Twenty drops weigh twenty times as much, so the same uncertainty is a twentieth of the answer. Counting many also averages out how differently each drop falls, and they do fall differently: the first from a full pipette is not the same as the last.
The figure belongs to one material and one dropper
A thick resinoid gives a heavier drop than ethanol from the same dropper. A different dropper gives a different drop of the same material. A warm room thins a viscous material and changes it again. So the figure you get here is true of the material you weighed, from the dropper you used, at the temperature you did it, and nothing else.
That is why it is not a conversion to keep using. Weigh each material once, turn the old note into grams, and throw the drop count away. A note in grams can be scaled, handed to somebody else and checked against a limit. A note in drops can do none of those.
What this calculator does not do
It does not know how much a drop weighs, and it will not guess. There is no standard drop to guess with: a figure found online is somebody else's dropper and somebody else's material. If you have not weighed your own, this has nothing to work from, which is the correct answer.