For a full 2,000-health bar at 100 effective armor, Ruby Crystal and Cloth Armor add equal physical durability when compared separately without other defensive effects. Cloth costs 100 gold less. Ruby adds health that can help against magic damage too. You still need to choose for the damage coming next.
Buy armor to reduce physical damage. Buy health to increase the health pool your defenses protect. They work together: more health makes each armor point cover more damage, while more armor makes each point of health last longer against physical hits. The best next purchase depends on your current stats, incoming damage and the item you are building toward.
Prices and item descriptions concern standard PC Summoner’s Rift. Worked examples isolate ordinary damage and defenses; they are not recorded fights or complete champion-build simulations.
First, separate damage type from champion labels
Armor reduces physical damage. Magic resistance reduces magic damage. Neither ordinary armor nor magic resistance reduces true damage. Additional health gives you more health to lose, but some attacks and abilities also calculate their damage from that larger pool.
"AD champion" is a poor substitute for inspecting the damage. A champion can deal more than one type, and an ability’s AD or AP scaling does not decide which resistance counters it. The relevant question is what damage reaches you, not which offensive stat the opponent bought.
Your lane opponent may be the biggest physical threat, but an enemy mage arriving at the next objective changes the purchase. If a physical-damage carry is doing almost all the damage you take, the cheaper armor component may let you survive the next exchange while keeping more gold toward another purchase.
A death recap full of physical damage can make Cloth look like the obvious fix. First, ask whether that death resembles the fight ahead. Being caught alone by three enemies may tell you little about the next organized fight. Plan for the enemies that can reach you, not a spell you expect to stay out of range of.
The health-and-armor calculation
For a target at full health with nonnegative effective armor, ignoring other defensive effects:
Physical effective health = health x (1 + effective armor / 100).
Effective health means the amount of damage before armor reduces it needed to use up that health pool. It is a comparison tool, not extra health displayed on the bar. Here, effective armor is the armor actually used after any relevant enemy penetration or reduction. The community wiki’s armor reference documents the formula.
At 100 effective armor, ordinary physical damage is halved. With 2,000 health, that makes the calculation 2,000 x 2 = 4,000: you need 4,000 damage before armor to exhaust the full bar. For now, leave out shields, healing, other damage reduction, true damage and effects that scale with the target’s health.
A Ruby Crystal and Cloth Armor can tie
Current Ruby Crystal gives 150 health for 400 gold. Cloth Armor gives 15 armor for 300 gold. Apply each separately to that hypothetical 2,000-health, 100-armor champion, with no penetration:
| Purchase | Stats after purchase | Physical effective health |
|---|---|---|
| Neither | 2,000 health; 100 armor | 4,000 |
| Ruby Crystal | 2,150 health; 100 armor | 4,300 |
| Cloth Armor | 2,000 health; 115 armor | 4,300 |
Cloth Armor reaches the same physical-only result for 100 less gold in this example. Ruby Crystal also adds health against the rest of the damage profile. Check the recipe you are working toward, too. A spare Cloth Armor may delay a needed item whose recipe uses Ruby Crystal instead. These starting stats are a comparison, not an assumed first-recall stat line for every champion.
Now compare each purchase separately from two different starting points. First, change the starting health to 3,000 while keeping armor at 100. Ruby adds 300 physical effective health, but Cloth adds 450. Next, start at 2,000 health and 200 armor instead. Ruby adds 450 physical effective health while Cloth adds 300. The stat you already have changes what the other stat can do for you.
Do not chase a universal health-to-armor ratio from these two prices. The calculation leaves out other damage types, inventory space and the finished item you need.
Does armor have diminishing returns?
The displayed reduction percentage rises more slowly as armor increases. That does not mean each armor point adds less absolute physical effective health to the same health pool.
At 2,000 health, going from zero to 100 armor raises physical effective health from 2,000 to 4,000. Going from 100 to 200 armor raises it from 4,000 to 6,000. Both gains add 2,000. The second is a smaller percentage increase over what you already had, but it has not added fewer points of physical effective health.
Armor has not stopped working at 100. The next armor purchase still has to compete with health, magic resistance and the effects on other items.
Add magic damage and the comparison changes
Return to 2,000 health and 100 armor, now with 100 magic resistance too. Start at full health and take a pair of hits: 1,000 raw physical damage and 1,000 raw magic damage, with no penetration or other modifiers. Apply the resistance formulas separately to the two damage types.
Before either purchase, each hit deals 500 after its resistance, for 1,000 damage in total. You have 1,000 health left. Keep both incoming hits fixed while applying each purchase separately below.
With a Ruby Crystal, those hits still deal 1,000 combined damage, but your larger full health pool leaves 1,150 health. With Cloth Armor, the physical hit is 1,000 / 2.15, about 465.12 damage, while the magic hit stays at 500. You finish at about 1,034.88 health. These displayed values are rounded after the calculation.
That is not a contradiction of the earlier table. The earlier table measured a complete physical-only health pool; this example asks how much health remains after one specified physical-and-magic hit pair. Armor cannot reduce the magic portion. Health helped against the combined damage here, though it cost more and does not reduce either hit itself.
Or buy magic resistance. If the mage is the immediate lethal threat, an MR component deserves a place in the comparison. The right answer can be neither Ruby nor Cloth.
Your champion may already supply one side of the equation
Cho’Gath gains maximum health when a successful Feast kill grants a stack. With more health from his kit, the same resistance purchase protects a larger pool. That is a reason to consider armor or MR against the appropriate threats, not a reason to avoid health on every finished item.
Malphite has a different interaction. Thunderclap increases his armor, with a stronger effect while Granite Shield remains active. Do not judge his armor from his inventory alone. If your plan is to survive an extended fight, include the period after that shield breaks rather than judging the whole fight from his shielded armor.
Restored health matters too. If a fixed 200-health heal is actually received, it restores a pool that armor can protect from future physical damage. At 100 effective armor, that restored health can absorb 400 raw physical damage under the same simplified rules. The heal does not become larger; the restored health takes more physical damage to remove.
Only count the healing you can receive in time. A teammate on the other side of the fight may not reach you, and a heal used while you are nearly full cannot replace as much lost health. Having a healer on your team does not guarantee that the heal reaches you during the engage.
Percentage-health damage needs a more careful answer
Percentage-health damage is not a fourth damage type. An effect can calculate a percentage of health and still deal physical, magic or true damage. Armor remains relevant to a physical percentage-health effect; magic resistance remains relevant to a magical one.
Vayne’s Silver Bolts deals maximum-health true damage. Patch 26.17 changed its percentage and minimum damage, but not that basic distinction. Armor does not reduce the true-damage portion. Increasing maximum health also increases the amount calculated by that percentage.
For an isolated effect dealing 10% of the target’s maximum health as true damage, raising that target’s health from 2,000 to 2,400 changes the hit from 200 to 240. It still takes 10% of the bar. This calculation deliberately excludes minimum damage, attacks between procs and every other effect in an actual Vayne fight.
It does not follow that all defensive stats are useless against Vayne. Her ordinary physical damage still goes through armor, and health still affects how much of that damage you can survive. Preventing attacks, forcing her away or ending the fight sooner can matter more than trying to solve Silver Bolts with a single defensive stat.
Against a fixed amount of true damage that does not increase with your health, additional health does provide a larger buffer. Keep those two cases separate: 300 true damage is not the same threat as a true-damage effect that grows with your maximum health.
Buy the full item, not the spreadsheet row
Current Plated Steelcaps has 25 armor, 45 movement speed and a 1,200-gold price, plus a passive described as reducing incoming attack damage by 10%. That passive is distinct from the armor stat; it is not a generic 10% reduction to every enemy spell.
Movement speed may help you leave attack range or avoid a skillshot altogether. That benefit never appears in a stationary effective-health calculation. Read the rest of the item before comparing only its armor number.
On your next recall, make the choice in this order:
- Identify the damage you must survive next, including the enemies likely to reach you.
- Check the health and resistances you already have, including temporary kit effects.
- Compare the actual components you can afford and the finished items they lead toward.
- Read the relevant passive or active instead of treating the item as a pile of stats.
If penetration is distorting an armor comparison, use the armor remaining after it applies; the lethality guide works through that calculation separately. For the purchase itself, protect the health you already have against the damage you expect next. Against the physical-only example, Cloth bought the same extra durability for less gold. Once the magic hit arrived, Ruby left more health. Change the incoming fight and you change the answer.