Minecraft protection enchantment

Solution 1:

A full set of Leather Armor gives 7 'armor points', while a full set of Iron Armor gives 15. (Each armor point gives a 4% damage reduction, so Leather Armor reduces all damage by 28% and Iron Armor by 60%).

The Protection enchantments are actually fairly complicated (at least, more complicated than the standard armor formula). Each enchantment has a certain value which the Minecraft Wiki calls the EPF (Enchantment Protection Factor). Whenever you take damage, the EPF of all of your enchantments are added together to a max of 25, which is then multiplied by a random number between 0.5 and 1, and lowered down to 20 if it was above it. The remaining number is then added to your armor points (so, 4% damage reduction per point)

Every enchantment has a different EPF number, which you can find here. Protection III has an EPF of 3.

With a full set of Protection III Leather Armor, you will have a base EPF of 12 (3 EPF x 4 pieces of armor). This means the minimum amount of damage reduction you will get is 52% (28% for the armour, 12 x 0.5 x 4% = 24% for the enchantments). The maximum, though, is 76% (12 x 1 x 4% = 48%). So, on average a full set of Leather Armor with Protection III will give you 64% damage reduction, while a full set of unenchanted Iron Armor will give you 60%.