These are the default levels for monsters:
Level	Ave HP	Ave Dam
15	250	      20
20	350	      22
25	475     	24
30	600     	27
35	680     	30
40	790     	33
45	900     	37
50	1300	    41
55	1650    	45
60	2000    	50
65	2800    	55
70	3500    	60
75	4200    	66
80	5000    	72
85	6200    	78
90	7800    	85
95	10000   	92

These numbers are flexible.