Look for your main stat score (wiz it is int., sor it is chr. ect.) and cross it with the highest spell level you can cast.)
Each spell level cost 1 point per level (0 counts as 1/2).
You may only memerise (or cast in the case of bards and sorcers) your level+modifier. (A first leve wiz with a 16 int could cast a max of 4 0 level and 4 first but would only have 5 point)

Score	0	1	2	3	4	5	6	7	8	9	10
10-11	0
12-13	0.5	1.5
14-15	1	2	4
16-17	1.5	2.5	4.5	7.5
18-19	2	3	5	8	12
20-21	2.5	4.5	6.5	9.5	13.5	18.5
22-23	3	5	9	12	16	21	27
24-25	3.5	5.5	9.5	15.5	19.5	24.5	30.5	37.5
26-27	4	6	10	16	24	29	35	42	50
28-29	4.5	7.5	11.5	17.5	25.5	35.5	41.5	48.5	56.5	65.5
30-31	5	8	14	20	28	38	50	57	65	74	84

Level	Bard	Cleric	Druid	Paladin	Ranger	Sorcerer	Wizard
1	1	2.5*	2.5*			5.5*	2.5*
2	1.5*	4	4			7	4
3	2.5	6*	6*			8	6*
4	3.5*	9.5	9.5	0*	0*	15*	9
5	6.5	12.5*	12.5*	0	0	17	12*
6	8.5	17.5	17.5	1	1	28*	17
7	8.5*	23*	23*	1	1	32	22*
8	13.5	30	30	1*	1*	48*	29
9	16.5	37*	37*	1	1	55	36*
10	16.5*	46	46	3	3	74*	45
11	23.5	56*	56*	3*	3*	83	54*
12	27.5	67	67	6	6	106*	65
13	27.5*	80*	80*	6	6	117	76*
14	37	93	93	7*	7*	144*	89
15	43	109*	106*	7	7	157	102*
16	45*	124	124	13	13	188*	117
17	59	143*	143*	16	16	203	132*
18	69	160	160	17	17	238*	149
19	80	181	181	26	26	255	165
20	86	198	198	30	30	273	182