Increased Attack Speed

EIAS refers to how much to adjust the rate that an animation is played. Higher values of EIAS make an animation play faster.

Formulas

ΔEIAS = floor((120 * IAS) / (120 + IAS))
IAS = ceiling(120 * ΔEIAS / (120 - ΔEIAS))

Calculating necessary IAS from a target ΔEIAS

Necessary ΔEIAS = Target ΔEIAS - Skill ΔEIAS + WSM

From your target ΔEIAS, subtract any quantities of ΔEIAS from skills. This can come in the form of Skills that increase your attack speed such as Burst of Speed and Fanaticism and curses that slow your attack speed like Decrepify. Attack speed increasers have a positive ΔEIAS while speed decreasers have a negative ΔEIAS.

From that amount, add your weapon speed modifier (WSM).
-If you are single wielding, your weapon speed modifier is your weapon's WSM.
-If you are dual wielding and the weapon in your left inventory slot is your main weapon, your weapon speed modifier is (LeftWSM + RightWSM) / 2.
-If you are dual wielding and the weapon in your right inventory slot is your main weapon, your weapon speed modifier is (LeftWSM + RightWSM) / 2 - LeftWSM + RightWSM.

The resulting value is your Necessary ΔEIAS. This is the amount of speed increase you need to make up with the IAS from your equipment. If its value is negative, you don't need any additional IAS from your equipment. If it is positive, look up this value in the table below to get the amount of IAS you'll need to have in order to reach the Target ΔEIAS.

EIAS Conversion Table

ΔEIAS IAS 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 9 9 10 10 11 11 13 12 14 13 15 14 16 15 18 16 19 17 20 18 22 19 23 20 24

ΔEIAS IAS 21 26 22 27 23 29 24 30 25 32 26 34 27 35 28 37 29 39 30 40 31 42 32 44 33 46 34 48 35 50 36 52 37 54 38 56 39 58 40 60

ΔEIAS IAS 41 63 42 65 43 68 44 70 45 72 46 75 47 78 48 80 49 83 50 86 51 89 52 92 53 95 54 99 55 102 56 105 57 109 58 113 59 117 60 120

ΔEIAS IAS 61 125 62 129 63 133 64 138 65 142 66 147 67 152 68 157 69 163 70 168 71 174 72 180 73 187 74 194 75 200 76 208 77 215 78 223 79 232 80 240

ΔEIAS IAS 81 250 82 259 83 270 84 280 85 292 86 304 87 317 88 330 89 345 90 360 91 377 92 395 93 414 94 434 95 456 96 480 97 507 98 535 99 566 100 600

ΔEIAS IAS 101 638 102 680 103 728 104 780 105 840 106 909 107 988 108 1,080 109 1,190 110 1,320 111 1,480 112 1,680 113 1,938 114 2,280 115 2,760 116 3,480 117 4,680 118 7,080 119 14,280 120 ∞