If the player takes damage of a sufficient type, worn armour loses 1 durability, or more if the damage is at least 8.

The durability lost is calculated by rounding incoming damage down to the nearest multiple of 4, then dividing by 4. (If this calculation equals 0, it is changed to 1.)

⇒ e.g. 19 damage, rounded down to 16, then divided by 4 = 4 durability lost

Importantly, this is incoming damage, it is not calculated with the damage actually taken. 

The lowest durability armour piece in the game is the leather helmet (in game called leather cap), crafted from 5 leather with 55 durability. The next best option are leather boots, with 65 durability but only needing 4 leather to craft. Try to get 4 leather, but if you end up with 5, make a helmet. If you need leather for other goals, craft boots, it’s only 5 seconds slower than the helmet when using a campfire. 

Wearing multiple armour pieces does not affect the durability lost or incoming damage, it just affects how much damage you take as a player (irrelevant for campfires, since armour does not affect campfire damage). This means technically more armour can be better, if it saves a death cycle. 

Unlike tools, golden armour does not have the least durability, though it is second least after leather (and a gold helmet breaks faster than a leather chestplate). 

• Ruined portals have a 61.48% chance to have at least one enchanted gold armour piece, as well as having magma blocks for damage. 

Village tannery chests (tanneries have chests in all village types except desert) have an 80.63% chance to have at least 1 leather armour piece. 

• If you get unlucky or have iron and no tannery, you can still trade/reroll with a novice leatherworker for dyed leather pants (3 emeralds).

Shipwreck food chests have a 55.67% chance of having at least 1 enchanted leather armour piece. 

• Or going to the BT has a 16.7% chance of having a leather chestplate (63.1% chance of getting leather armour from either ship or BT)

If you get armour from a shipweck or a ruined portal, pay attention to the enchantment it comes with.

THORNS

Armour with the Thorns enchantment will take 2 durability for every time the enchantment successfully deals thorns damage (higher chance for higher levels of the enchantment). This weights it slightly more towards mobs, but nothing crazy.

UNBREAKING

The Unbreaking enchantment gives a chance not to use up durability. On average, leather armour with Unbreaking III is effectively the same as gold armour. A leather helmet with Unbreaking I breaks faster on average than leather chestplates and pants. 

FROST WALKER

Wearing boots enchanted with Frost Walker will make you immune to any damage from magma blocks or campfires (including soul campfires). You can still take fire damage from fire blocks and lava, meaning fns is still viable.

PROTECTION

Protection and its subtypes (e.g. Fire Protection) reduces damage taken but not durability lost. 

MENDING

Mending shouldn't be a problem unless you let it. After respawning, make sure you pick up xp before re-equipping your armour piece. 

CURSE OF VANISHING

This will marginally slow you down, but make sure you throw the item before you die (this should be fairly easy, hover over the armour slot and press Q when you reach half a heart). 

⇒ Dying is the quickest way to reset your health, but takes a mechanical penalty in re-equipping the armour and recommencing the damage source. There is also a 1 second delay before you can respawn, so the more saturation the player can get and the lower the damage between 0 and 8 the better.

• For this reason, soul campfires are not better than regular campfires. They do double the damage (2) but come at the same durability cost. However, you could use them to get around I-frames by alternating normal + soul. 

• Eating food to avoid/delay dying can save this time. Campfires will break a leather helmet in 27 seconds, so if you stay alive (with good food/gapples) this is the time you’d reach. (Resistance from e-gaps doesn’t reduce incoming damage for the purpose of durability loss). 

• Respawn with beds, charged respawn anchors or use the world spawn. For leather helmet on magma, you only need two charges on the respawn anchor. 

Campfires are a good option, dealing 1 damage every tick. Due to invincibility frames, this is reduced to 1 damage every 0.5 seconds, meaning 1 durability lost per half second. These can be found naturally on the pie chart in taiga villages, or easily crafted.

Magma blocks also deal 1 damage every tick, which also amounts to 1 durability every 0.5 seconds. Damage from magma can be reduced by armour, but the damage reduction with just leather boots/helmet is negligible (but taking less damage is better). You can find these naturally at ruined portals and in the nether. 

Fns/Fire Charges are basically the same as magma except they (1) set you on fire and (2) can burn items. Ongoing burning damage does not affect armour durability, so you should extinguish and relight so you don’t burn. When low, try to let yourself burn to death otherwise you will end up on half a heart and have to die a different way to avoid burning your armour. (You need a comfortable number of fire charges, probably from a bastion.)

Cactus also deal 1 damage every 0.5 seconds, making them a good option for if you have a desert. To avoid your armour piece hitting the cactus when you die, you can do the same thing as for a Curse of Vanishing armour piece (above) and hover in your inventory ready to press Q before you die. You can throw it towards your bed in order to pick it up and instantly begin to break it again. 

Iron golems can deal up to 32.25 damage on Hard mode. Even though the player only has 20 health, that damage is still taken in full when considering durability loss (so max 8 durability lost per hit). However, the damage dealt is random, being anywhere between 11.25 and 32.25 damage on Hard. This means while iron golems can be quicker than campfires, they can also be inconsistent.  

• (Can overlap with die to iron golem and take 200 damage; punching the golem on respawn can damage it to save time killing it later; does not require crafting campfire)

• Since you lose durability regardless of the damage actually taken, you can overlap campfire with iron golem to take more durability when you’re about to die. 

Zombies/Skeletons/Creepers/Spiders – For zombies, skeletons and spiders, there is no point to change difficulty from Easy. You just die quicker. Creepers can deal up to 64.5 damage on Hard (16 durability vs max 5 on Easy and 10 on Normal), so if you are using mobs and you are low health, toggle hard and run inside a creeper. 

Stalactites (and sulfur spikes) lower armour durability when they fall on you, but it’s a bit more complex. A falling stalactite deals 6 damage for every block between the dripstone and the floor, capping at 40 damage. This means the maximum should be 10 durability from 1 dripstone (as can be seen by the red line below). However, helmets reduce the incoming damage by 25% while also taking more durability themselves. The way this works is that 

• the helmet loses the durability from the incoming damage (40 —> 10), and then:

• all armour loses durability for 75% of the damage (30 —> 7). So the helmet takes a max 17 durability while other armour worn takes max 7 (as seen by the blue and yellow lines below).