Life Steal is an offensive stat that applies to auto-attacks and grants healing equally with a percentage of the dealt damage. Unless otherwise specified, it usually applies at 100% damage dealt effectiveness. It doesn’t work not for item actives or on inhibitors, turrets or nexuses.

All the champions begin the game with 0% Life Steal and work their way up using items, runes and abilities based on their interest in the game. Some champions use Life Steal by default because it is built into their kit.

Before we get into the specifics, it's important to make the differences between Life Steal and Vamp Effects. All heal but not in the same way.

Omnivamp applies to all sources of damage (basics, abilities, and item actives). It grants healing equal to a percentage of the physical damage, magical damage or true damage dealt and items such as Eclipse, Goredrinker, Ravenous Hydra, and jungle items (Emberknife, Hailblade) can be used to increase it.

Physical Vamp only applies to physical damage dealt by basics and abilities. Use Elixir of Wrath to boost it by 12% for 3 minutes.

Spell Vamp was removed from items in 2016, but it is still available in some champion’s kits, like Lee Sin’s W. It applies to abilities and grants healing equal to a percentage of the damage dealt by the ability.

So, long story short:

Life Steal: healing from basic attacks
Omnivamp: healing from everything (basics, abilities, items actives)
Physical and Spell Vamp: healing from physical damage and from ability damage

HOW TO CALCULATE LIFE STEAL?

It’s determined by the amount of damage you deal and the damage reductions your opponent has. For example, you may deal 200 damage with a 25% Life Steal, but if your enemy has a 50% damage reduction, you’ll receive half the healing you should get

Also, because Life Steal can stack and multiply, the passives of some items should be taken into account. Spirit Visage’s passive increases all healing by 25%, so, if you have, let’s say 10% Life Steal, you should calculate as follows:

10% x 1.25 = 12.5% Life Steal

The maximum amount of Life Steal’s healing one can get in a game is 220% on Sion, considering the buffs he gets from Glory in Death.

LIFE STEAL ITEMS

Life Steal can be very effective for aggressive champions such as assassins and AD carries.

Vampiric Scepter

It gives 7% Life Steal and 15 attack damage, making it a great early game item. It provides good sustain, and because it’s a component for other Life Steal items, like Bloodthirster and Blade of the Ruined King, it’s often a good idea to take it as soon as possible.

Bloodthirster

A good option for ADCs and AD champions like Yasuo and Yone. It grants you 55 attack damage, 20% critical strike chance, and 18% Life Steal. The life you steal with attacks can overheal you. No, you don’t just simply get more HP, but you get a 50-320 shield that decays slowly within 25 seconds if you don’t deal or take some damage.

Blade of the Ruined King

A legendary item for those who prioritize damage and attack speed. You gain 40 attack damage and 25% attack speed, plus the additional damage and movement speed from its passive. The amount of Life Steal is quite low, only 7%, but given the damage, AD champions like Gnar, Trundle, Tryndamere or Sett should be fine.

Also, considering the 25% Attack Speed, ADCs like Ashe, Twitch or Varus can benefit from this item's Life Steal by attacking from a long distance.

Immortal Shieldbow

An item with everything mentioned above: 50 Attack Damage, 20% Attack Speed, 20 Critical Strike Chance and 7% Life Steal. In addition, if you take damage that reduces your HP below 30%, the item grants you a 250-630 shield for 3 seconds and 15-35 Attack Damage for 8 seconds.

Because of the Critical Strike, this item is particularly useful for Marksmen such as Jinx, Varus, and Kalista.

BEST CHAMPIONS WITH LIFE STEAL IN THEIR KIT

Buying items is the most common way to obtain Life Steal, but some champions already have the ability to steal life built into their kit. This ability is their signature.

Warwick

Warwick does not have “Life Steal” but his passive, Eternal Hunger, effectively acts like it when he’s below half health, healing him for up to 250% of the on-hit damage applied by it. Similarly, his Q deals damage based on his opponent’s hit points and heals Warwick for a percentage of that damage. When paired with real Life Steal items (or Omnivamp in the case of Ravenous Hydra), Warwick can effectively drain tank his enemies.

Warwick’s play style is fairly simple. You use his W and speed to get to a low HP enemy and use Q to both kill them and steal their life. This can be especially useful when ganking because he can easily take down enemies with low HP. Finally, Warwick’s ultimate gives him the same pseudo-Life Steal as his passive, as it heals him for 100% of the post-mitigation damage. You can use Infinite Duress to jump to a target, becoming immune to crowd control mid-flight, and heal off the damage you deal to the target.

Nasus

Nasus’ passive gives him Life Steal, between 10 to 22% based on your level. This is important for him early in the game because it allows him to stay in lane and stack up his Q, Siphoning Strike, by killing minions. Once he gets a decent amount of damage, his Life Steal increases as well, allowing you to win duels with your empowered Qs. Also, if the enemy pushes you under your tower, Nasus can take advantage of the situation by using his Life Steal to drain the enemy’s hit points while they are being shot by the tower.

Nasus is one-of-a-kind; he’s a tank with Life Steal potential, which means in the late game he can become near-unkillable and shut down any enemy with his Q.

Olaf

Similar to Warwick, Olaf’s passive gives him Life Steal when he’s under a hit point threshold. In Olaf’s case, his passive grants him up to 30% Life Steal (based on his level) when he has at least 70% missing HP. This makes him an aggressive early game jungler. If he gets into a fight with the other team's jungler, he can use his passive to turn the tide over an extended fight.

I'd also like to point out that his E functions similarly to Life Stealing. Olaf must sacrifice some HP to use his E, but if he kills the target, he recovers the amount of HP he sacrificed.

WHEN TO USE LIFE STEAL

If you want to survive fights and win your lane, healing is essential in every game. If you have Life Steal in your kit or can make it with items, use it to your advantage. It's a useful stat that provides sustain to champions who don't have it.

If you have low HP and believe you are an easy target for sneaky enemies, think twice. What are you afraid of if you have a good amount of Life Steal? Poke them as much as you can when you have a range champion and try to lead them under your tower with close range champions. You can also trick enemies into fights they believe they will win, but your Life Stealing kicks in and they lose HP while you gain strength.

Also, before deciding to build Life Steal if your champion does not have it by default, consider the enemy team and your position. Prioritize Critical Strike items, for example, if you have an ADC who excels at that. You can use Vampiric Scepter in the early game to poke while keeping your HP up.

Life Steal items may be useful in some situations, such as when the enemy team is full of tanks. It's even better if you are playing a range champion. Allow them to come; you'll drain their life from afar. Other times, Life Steal items may be ineffective if you lack the required damage to win the fight. It's pointless to be able to restore HP if enemies can just one-shot you.

And don't forget to buy attack speed items along with Life Steal items. You'll recover your HP faster this way.

CONCLUSIONS

Overall, Life Steal gives you a significant advantage in lane and fights, but you must consider your situation before using Life Steal items. If you have a high damage potential and a high score, you can use Life Steal to secure a kill faster and make it more difficult for enemies to force you to go back. It is also useful if the enemy lacks CCs to shut you down. But, if you fully focus on Life Steal and ignore the other stats that are important for your role (like critical strike for Marksmen), you will become an easy target, which will be detrimental to your entire team.