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	ΔEIAS	IAS	ΔEIAS	IAS	ΔEIAS	IAS
1	2	31	42	61	125	91	377
2	3	32	44	62	129	92	395
3	4	33	46	63	133	93	414
4	5	34	48	64	138	94	434
5	6	35	50	65	142	95	456
6	7	36	52	66	147	96	480
7	8	37	54	67	152	97	507
8	9	38	56	68	157	98	535
9	10	39	58	69	163	99	566
10	11	40	60	70	168	100	600
11	13	41	63	71	174	101	638
12	14	42	65	72	180	102	680
13	15	43	68	73	187	103	728
14	16	44	70	74	194	104	780
15	18	45	72	75	200	105	840
16	19	46	75	76	208	106	909
17	20	47	78	77	215	107	988
18	22	48	80	78	223	108	1080
19	23	49	83	79	232	109	1190
20	24	50	86	80	240	110	1320
21	26	51	89	81	250	111	1480
22	27	52	92	82	259	112	1680
23	29	53	95	83	270	113	1938
24	30	54	99	84	280	114	2280
25	32	55	102	85	292	115	2760
26	34	56	105	86	304	116	3480
27	35	57	109	87	317	117	4680
28	37	58	113	88	330	118	7080
29	39	59	117	89	345	119	14280
30	40	60	120	90	360	120	infinity