OK, I took 2 vanilla installs of Minecraft versions 1.12.2 and 1.13.2, for comparison.
Java uses 2.4 gb to run MC 1.12.2,
While Java uses 3.6 gb to run MC 1.13.2,
So, I can assume modded Minecraft version 1.13.2 will use more ram than other versions of Minecraft, depending on the mods used.
Java 8 on Linux Ubuntu 16.04.
cheers.
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