Attack speed (AS or ASPD) is a stat that is the frequency of a unit's basic attacks. They are measured and displayed as attacks per second.
Each champion starts with a certain attack speed ratio, which is also the value given by default to their base attack speed (attack speed at level 1 without any other bonuses). Some champions can start with a base attack speed different from their attack speed ratio. Additional bonus attack speed can be obtained through levelup or with a variety of items, abilities and runes. Bonus attack speed stacks additively, and each bonus point acquired directly affects its statistic. Bonus attack speed is a percentage of the attack speed ratio, therefore, champions with higher ratio benefit more from bonus attack speed.
Attack speed is capped at 2.5 attacks per second (or 1 attack every 0.4 seconds). It also cannot be reduced below a floor of 0.2 (or 1 attack every 5 seconds). The values of these restrictions can be altered by certain effects.
Calculations
Bonus attack speed per level
Champions gain bonus attack speed % every time they level up, which ranges from roughly 0  6% (the exact number depending on the specific champion) and can be calculated through the statistics growth formula.
Bonus AS% stacks additively.
 Example: grants +35% attack speed and grants +50% attack speed, so the champion gains +85% in total.
Notes:
 Final attack speed cannot go above the cap of 2.5 attacks per second, unless it is ignored by some effects.
 Many ingame tooltip percentages (such as runes) have been rounded, so results may be slightly different unless the precise numbers are known.
Example
 base attack speed and attack speed ratio are both 0.651.
 Calculating "bonus attack speed":
 Every time statistics growth formula.
 At level 10 he has gained 3.22% × 9 × (0.7025 + 0.0175 × 9) = 24.9228% as bonus AS%.
levels up, he gains bonus AS% based on his percentage growth 3.22% and his level through the  Let's say he has maxed increasing his attack speed by 40%.
 He also has the rune to 3%.
 And he has : +35%.
 All together he has: 24.9228% + 40% + 3% + 35% = 102.9228% bonus AS%.
 Every time statistics growth formula.
 Final calculation:
 0.651 × (1 + 102.9228 ÷ 100)
≈ 1.321027428
 In game, the number will be shown as: 1.321.
 0.651 × (1 + 102.9228 ÷ 100)
Exceeding or altering the attack speed cap
The following game elements will exceed or alter the 2.5attackspersecond cap:
Removing the cap
Effects that remove the attack speed cap allow characters to fire basic attacks at rates higher than 2.5, given high enough attack speed bonuses. The cap is technically increased to 90.0 for the duration, however limits to the game itself only allow for up to 30 attacks per second, or one per frame.
Champions
Runes
Fixed attack speed above the cap
Champions
  This has a fixed attack speed of 3.0. It does not interact with bonuses nor the attack speed stat itself.
Reducing the cap
Champions
  Special attack cooldown and attack speed calculation  cannot reach 2.5 attack speed.
  Always fixed to his base attack speed + innate attack speed growth, thus can never reach 2.5 attack speed.
  Reduces the cap to 1.75 and increases the floor to 1.75 until the effect ends. Effects that remove the attack speed cap (see above) still allow exceeding the cap.
Attack speed as scaling
The major part of champion abilities that use attack speed will scale with base attack speed. But some abilities scale with the total or bonus attack speed the champion has.
Note that any (bonus) attack speed exceeding the attack speed cap will still improve these ability scalings, as they are not depending on the absolute attack speed stat.
Champions
 and
Increasing attack speed
Items
Flat Attack Speed
Item  Cost  Amount  Availability 

1100  35 %  All maps  
3300  25 %  All maps  
1625  50 %  Summoner's Rift  
300  12 %  All maps  
3100  25 %  All maps  
700  15 %  All maps  
3300  40 %  All maps  
3000  50 %  All maps  
2600  30 %  All maps  
2600  30 %  All maps  
1000  25 %  All maps  
2600  40 %  All maps  
2600  40 %  All maps  
1100  35 %  All maps  
3200  15 %  All maps  
3733  40 %  All maps  
3733  50 %  All maps  
2900  50 %  All maps  
1400  12 %  All maps 
Conditional Attack Speed
Item  Cost  Total Amount  Availability 

2300  10%  30%  All maps  
3100  25%  73%  All maps  
3100  20%  80%  All maps 
Champion abilities
Allytargeted
User only
 and
 and
 and
 and
Runes
Decreasing attack speed
Champion abilities
Items
Champions with altered base attack speed at level 1
List of champions' attack speed
Champion Level  Top 5 champions  Bottom 5 champions  

Level 1  1.  0.8 AS  1.  0.475 AS 
2.  0.751 AS  2.  0.571 AS  
3. 3. 3.  0.736 AS  3.  0.579 AS  
4. 4.  0.721 AS  4.  0.613 AS  
5.  0.711 AS  5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5. 5.  0.625 AS  
Level 18  1.  1.263 AS  1.  0.678 AS 
2.  1.166 AS  2.  0.692 AS  
3.  1.105 AS  3.  0.713 AS  
4.  1.086 AS  4. 4. 4. 4.  0.731 AS  
5.  1.083 AS  5.  0.745 AS 
Notes
 All percentages listed in a champion's attack speed statistic are approximations.
 Many abilities can scale indirectly with attack speed (for example, through the flat cooldown reduction per attack with ).
Trivia
Last updated: December 8, 2019 – V9.23
 The most attack speed a champion can have is 10.125 with a level 18 .
 Base AS: 0.625 AS
 Items:
 One
 One
 Four
 Runes:
 Buffs:
 AS Amplification:
 Relevant mathematics:

 Items = 353% bonus AS + + =
 Runes = 10% = 138% bonus AS + +
 Buffs = 219% bonus AS + + + + + =
total AS:
 3.53 + 1.38 + 2.19)) × = 10.125 total AS total AS = (0.625 × (1 +

Last updated: December 8, 2019 – V9.23
 The most attack speed a champion can reach at level 1 with the initial 500 is 4.0796 with .
 Base AS: 0.658 AS
 Item:
 One
 Runes:
 (no stack)
 Attack speed rune shard
 Buffs:
 Relevant mathematics:

 Items = 12% bonus AS =
 Runes = 10% = 123% bonus AS + +
 Buffs = 385% bonus AS + + + + =
total AS:
 0.12 + 1.23 + 3.85)) = 4.0796 total AS total AS = (0.658 × (1 +

Offensive  Ability power · Attack damage · Attack speed · Critical strike chance · Critical strike damage · Armor penetration · Magic penetration · Life steal · Spell vamp · True damage 

Defensive  Heal and shield power · Health · Health regeneration · Armor · Magic resistance · Tenacity · Slow resist 
Utility  Cooldown reduction · Energy · Energy regeneration · Mana · Mana regeneration 
Other  Experience · Gold generation · Movement speed · Range 