Attack damage

Attack damage (or AD) directly increases the physical damage of a unit's autoattack and also improves the damage a small number of champion abilities do. Every champion starts with some base attack damage that increases each level. Additionally, several items and champion abilities, as well as spells, buffs, runes and masteries grant bonus attack damage. The champion's total attack damage is the base attack damage plus the bonus attack damage. This statistic stacks additively in most circumstances. When there are percentual attack damage bonuses, they are first added together if more than one and then they multiply the total attack damage (barring these percentual bonuses) of the champion.

At level 18, base attack damage ranges from 90.8 to 130 ( and ).

Champion abilities
Note: Only the attack damage bonus effect of these abilities is shown here, to read more information on each of these abilities, follow the link on each of them.
 * increases his attack damage by 60 / 75 / 90 for 7 seconds.
 * increases his attack damage by 40 / 55 / 70 / 85 / 100 + 0.4 / 0.55 / 0.7 / 0.85 / 1 per 1% health he is missing for 5 seconds.
 * passively increases his attack damage by 8 / 10 / 12 / 14 / 16. He can also activate this ability to increase his attack damage for 7 seconds by 14 / 22 / 30 / 38 / 46 instead, also increasing nearby allied champions' attack damage by half of that amount for the duration.
 * increases his attack damage by 30 / 40 / 50 / 60 / 70 for 20 seconds.
 * increases an allied unit's attack damage by 14 / 23 / 32 / 41 / 50 for 5 seconds.
 * increases his attack damage by 20 / 25 / 30 / 35 / 40% for 6 seconds.
 * passively increases his attack damage by 15 / 20 / 25 / 30 / 35 when the ability is not on cooldown and grants double that bonus for 10 seconds on activation. It is possible to have both bonuses activated if the cooldown gets refreshed during those 10 seconds
 * grants him 6.375% of the damage it deals as attack damage.
 * grants him 15 / 25 / 35 / 45 / 55 attack damage as long as he is on the trail created by the ability.
 * increases his attack damage by 7 / 14 / 21 / 28 / 35 + 1% of his max health for 6 seconds.
 * increases her attack damage by 1.5 / 2 / 2.5 / 3 / 3.5 when she is hit by an attack or hits an enemy. This buff lasts for 5 seconds and stacks up to 10 times. She can activate this ability to gain max stacks.
 * passively increases his attack damage by 25% of his armor.
 * increases her attack damage by 20% for 15 seconds.
 * increases his attack damage by 25 / 35 / 45 / 55 / 65 for as long as the ability is toggled on.
 * increases the attack damage of nearby allied champions by 4 / 8 / 12/ 16 / 20 while active and persists for two seconds after deactivation.
 * increases his attack damage by 30 / 50 / 70 and half of that to nearby allied champions for 10 seconds.
 * increases his attack damage by 20 / 25 / 30 / 35 / 40 for 8 seconds.
 * passively increases his attack damage by 5 / 10 / 15 / 20 / 25 + 0.15 / 0.20 / 0.25 / 0.30 / 0.35 per 1% of his health missing.
 * increases his attack damage by 15 / 25 / 35 for the next 5 / 6 / 7 attacks within 12 seconds.
 * increases her attack damage by 25 / 40 / 55 for 10 seconds.
 * increases his attack damage by 8 / 12 / 16 / 20 / 24 while active.

Masteries

 * increases your champion's attack damage by 1 / 2 / 3.
 * increases your champion's attack damage by .125 / .25 / .375 / .5 per level.

Runes

 * and runes increase attack damage.

Neutral buffs

 * The buff grants 40 bonus attack damage for 4 minutes.

List of champions' attack damage
† increases his attack damage by 25% of his armor. This includes his base armor and is an innate passive ability thus essentially increasing his base damage unlike all other ranked champion abilities which are temporary or situational boosts to damage. The increase to his damage is 5.25 at level 1 for a total of 60.57 and 19.75 at level 18 for a total of 136.22. {C ‡ increases his attack damage by 8/10/12/14/16. This is a ranked ability and thus could not be counted on for a bonus at level 1. However, arguments could be made that at level 18 you will have 5 ranks and thus this will increase his damage permanently by 16. This would put total attack damage at 124 damage, surpassing  for third place. Similarly, raises Master Yi's total attack damage to 146 damage passively,  passively raises Tryndamere's total attack damage by at least 25 points to a minimum of 142 at level 18.

Trivia
Besides with  (due to his ), the maximum attack damage any champion can get at level 18 is 1364, being  with  active, all  runes and the  and  masteries with  on cooldown, a fully stacked  and 5 other fully stacked, while having the , , , , ,  and  buffs.