APPROXIMATE HARDNESS CONVERSION NUMBERS FOR STEEL*

Brinell
Indentation
Diameter
mm
Brinell Hardness
Number
Rockwell Hardness
Number
Tensile
Strength
(approxi-
mate)
1000 psi
Standard
Ball
Tungsten-
Carbide Ball
B Scale
C Scale
2.45
627
58.7
347
2.50
601
57.3
328
2.55
578
56.0
313
2.60
555
54.7
298
2.65
534
53.5
288
2.70
514
52.1
274
2.75
495
51.0
264
2.80
477
49.6
252
2.85
461
48.5
242
2.90
444
47.1
230
2.95
429
429
45.7
219
3.00
415
415
44.5
212
3.05
401
401
43.1
202
3.10
388
388
41.8
193
3.15
375
375
40.4
184
3.20
363
363
39.1
177
3.25
352
352
37.9
171
3.30
341
341
36.6
164
3.35
331
331
35.5
159
3.40
321
321
34.3
153
3.45
311
311
33.1
149
3.50
302
302
32.1
146
3.55
293
293
30.9
141
3.60
285
285
29.9
138
3.65
277
277
28.8
134
3.70
269
269
27.6
130
3.75
262
262
26.6
127
3.80
255
255
25.4
124
3.85
248
248
24.2
120
3.90
241
241
100.0
22.8
116
3.95
235
235
99.0
21.7
114
4.00
229
229
98.2
20.5
111
4.05
223
223
97.3
104
4.10
217
217
96.4
103
4.15
212
212
95.5
100
4.20
207
207
94.6
99
4.25
201
201
93.8
97
4.30
197
197
92.8
94
4.35
192
192
91.9
92
4.40
187
187
90.7
90
4.45
183
183
90.0
89
4.50
179
179
89.0
88
4.55
174
174
87.8
86
4.60
170
170
86.8
84
4.65
167
167
86.0
83
4.70
163
163
85.0
82
4.80
156
156
82.9
80
4.90
149
149
80.8
73
5.00
143
143
78.7
71
5.10
137
137
76.4
67
5.20
131
131
74.0
65
5.30
126
126
72.0
63
5.40
121
121
69.0
60
5.50
116
116
67.6
58
5.60
111
111
65.7
56

This table, which is based on ASTM A370-68, Table III, lists the approximate relationship of hardness values to corresponding approximate tensile strength values of steels. Some compositions and processing histories may deviate from these relationships. The data in this table do not represent hardness-to-tensile strength conversions for austenitic, ferritic, and martensitic stainless steel. If more precise conversions are required, they should be developed for each specific composition and heat treatment. Related Rockwell superficial hardness numbers, if of interest, may be found in ASTM A370-68.