When you drink this potion, you gain the “enlarge” effect of the enlarge/reduce spell for 1d4 hours (no concentration required). The red in the potion’s liquid continuously expands from a tiny bead to color the clear liquid around it and then contracts. Shaking the bottle fails to interrupt this process.
RollQuest ships the D&D 2014 SRD as a content pack, on a 5e character sheet that does the maths - roll from the sheet and let the numbers work themselves out. Free to start.