Attack Speed Mechanics

Calculating your ApS is simple. The two factors are multiplied together, and your ApS is calculated in the following way:

For the rest of this article, this ApS value is referred to when ApS is mentioned. Before we go into how Attack Speed affects your damage per second (henceforth DPS), we must elaborate on how the AS% functions and what happens when you add different sources. Do note that certain skills, such as channeled abilities, do not benefit from Attack Speed in any way.

Attack Speed% is capped at 200% and further divided into two individual caps of 100%. For the sake of this article, we will call them “Cap 1” and “Cap 2”. That means that if you have 200% attack speed from Cap 1, you will only benefit from 100% of that attack speed. At the end of this section, you can see what Attack Speed sources belong to what cap. Make sure that you check what attack speed sources you have so you do not go over the cap!

Diablo 4's game engine is limited to checking the game state every 60 frames. In other words, every action in the game is calculated based on how many frames it takes for an action to happen, with the lowest being 1 frame and the highest having no cap. This means skills and abilities have different "frame times" at different ApS.

Using Rogue and Puncture as an example. The lowest ApS achievable for rogue is using two Swords with 1.1 Weapon ApS and no AS% from stats or paragon. Puncture at 1.1 ApS takes 26 frames to complete its full animation. You can convert this to Skills per Second (henceforth SpS) through the following formula:

SpS was theorized to be a hard cap of 5 skills per second. However, data collected shows that skills can go below that number. For example, Puncture has 10 frames at 2.9256 ApS which is achievable with daggers (1.2 weapon ApS) and 143.8% AS%. Using the formula above, 60/10 = 6 Punctures per Second, which disproves that 5 Skill casts per Second would be the hard cap for all spells.

Finally, how does ApS affect your DPS? Due to the limitations of the game engine, the game cannot handle ApS values that put us between frames. This forces breakpoints, where, unless you meet the next breakpoint, further increasing ApS does not increase your DPS.

Let us use a practical example for this. Puncture has one breakpoint at 1.9056 ApS and another at 2.07 APS. If you use daggers, any attack speed between 58.8% AS and 72.49% will be useless as it does not bring you over 2.07 ApS.

So between 58.8% Attack Speed and 72.5% Attack Speed, you will not benefit from AS%. This means that when optimizing your damage, you want to be aware of these breakpoints to ensure that you do not opt into AS% that is not necessary. In this example, if you were to have 60% AS and add 15% AS, you would go from the 15-frame breakpoint to the 14-frame breakpoint. This would result in a DPS increase of 15 Frames / 14 Frames = 1.0714 = 7.14%. Instead, if you get enough attack speed to go from the 15-frame breakpoint to the 13-frame breakpoint, it would be a Damage per Second increase of 15/13 = 1.1538 = 15.38%.

The issue with these breakpoints is that they do not follow the expected formula. The expected formula would have been the following:

Here is a list of some of the approximations that are based on real data collected from the game:

These approximations were created by testing Attack Speed breakpoints by increasing AS% by 1.3% or lower, from 0% to roughly 165% AS. Even then, these approximations are not perfect and are between 1-2% AS% off. To ensure as accurate breakpoints as possible, every skill has to be manually extracted by adding small increments of AS%. The approximations above are close to the Expected Required APS formula but slightly off, making it clear that something is affecting the frame timings.