My preference for this on the web is Wolfram Alpha: https://www.wolframalpha.com/input?i=57+tonnes+%2F+%286.1+g%...

(note I've slightly changed the prompt to match the "drums" OP used instead of barrels. This avoids the issue other child mentions of ambiguous units, as it clearly states the volume of drum it's using and gives options for others (e.g. the international 200L instead of the US 208L/55 GAL).

Another option which I wouldn't inherently trust to get the calculation just right, but is good for explaining the process if you can fact-check it is ChatGPT-4o: https://chatgpt.com/share/ead07fff-8d55-4147-a742-6e19b26f1e...