Source: Dungeon Master's Guide

Potion, rarity varies

When you drink this potion, your Strength score changes for 1 hour. The type of giant determines the score (see the table below). This potion has no effect on you if your Strength is equal to or greater than that score.

This potion's transparent liquid has floating in it a sliver of fingernail from a giant of the appropriate type. The potion of frost giant strength and the potion of stone giant strength have the same effect.

Type of Giant Strength Rarity
Hill Giant 21 Uncommon
Frost/Stone Giant 23 Rare
Fire Giant 25 Rare
Cloud Giant 27 Rare
Storm Giant 29 Legendary