How to calculate your IAS and FCR in Diablo 2

Due to the game’s mechanics, Increased Attack Speed and Faster Casting Rate do not scale linearly. Each second of a game consists of 25 ticks or frames, and casting spells or attacking always takes place at a new frame. Because of this, there are breakpoints to reach to increase casting and attacking speed by a single frame/tick.

Various attacks and spells have various base speed. Because of this, there are no general breakpoints for character classes, it is always dependent on the skill you are using and your class. If the casts or attacks have visuals, the best way to make sure additional IAS or FCR matters is by counting how many times your character performs the skill over a period of time.

As a baseline for most skills, i count the visuals for one minute which consists of 1440 frames. By dividing 1440 by the number of casts/attacks performed, you can get a fairly good estimate of your frame rate. You can repeat this once you have additional or lesser IAS or FCR on your character, and see if it increased, did not affect, or worsened your speed.

An example: I will use teleport as an example. Let’s say your character is a Barbarian who is wearing an enigma, and has 105% faster casting rate. Over the one minute, you will be able to cast teleport 180 times. A minute consists of 1440 frames. 1440/180=8, which is your teleport casting frame rate in this instance.

For some skills, like Whirlwind or Smite, counting the visuals is either challenging or impossible. For these skills, crushing blow visuals can be used to calculate your frame rate. By wear % Crushing Blow items and attacking an enemy for a considerable period of time, you can count how many crushing blows your character has performed over that period. With this method, you will need to know your exact Crushing Blow chance, and in case you kill the enemy fairly fast, you should try to reduce your damage during the testing or kill the same enemy multiple times so you gather additional data.

Depending on which skill you use, you might have 100% chance to hit an enemy, or it might come down to your attack rating. In case chance to hit comes down to your attack rating, you can see what chance you had by moving the cursor over your attack rating.

To determine the frame rate of Crushing Blows, multiplying your attack’s duration in seconds by 24 to estimate how many frames your attack have lasted, and divide it by the number of crushing blows you performed.

Calculate how many attacks you need to perform in order to cause a crushing blow by multiplying your crushing blow chance and hit chance.

By dividing the framerate of your crushing blows by the number of attacks needed for a crushing blow, you get your attack’s frame rate.

An Example: Let’s take Whirlwind as an example, Baal as the test enemy, 75% chance to hit based on your attack rating, and the duration of attacking one minute (=1440 frames). By wearing a Gore Rider and no other crushing blow items, you have 15% chance of causing it. If you caused 32 crushing blows,  your crushing blow frame rate is 1440/32=45. The chance of your attack to cause a crushing blow is 0.75×0.15=0.1125, or 11.25%. 1/0.1125=8.888, which means on an average 8.888 attacks are required for a crushing blow. 45/8.888 will be your estimated attack frame rate, which is 5,06 frames. You can repeat the test multiple times to get an accurate estimation on your exact attack framerate.


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