Improving Product Reliability and Software Quality, 2nd Edition

Appendix B

MTBF, FIT, and PPM Conversions

One of the most often used numbers in reliability is the mean time between failures (MTBF) number. MTBF represents the average time one can expect a device to operate without failing. There is no assurance that the consumer will realize this failure‐free time period because the MTBF is a statistical average. In fact, if a consumer experiences a failure, the likelihood of an additional failure is the same before the failure occurs as it is after the failure is repaired (Table B.1).

Table B.1 Conversion tables for FIT to MTBF and PPM.

FIT	MTBF	PPM
1	1,000,000,000	9
2	500,000,000	18
3	333,333,333	26
4	250,000,000	35
5	200,000,000	44
6	166,666,667	53
7	142,857,143	61
8	125,000,000	70
9	111,111,111	79
10	100,000,000	88
20	50,000,000	175
30	33,333,333	263
40	25,000,000	350
50	20,000,000	438
60	16,666,667	526
70	14,285,714	613
80	12,500,000	701
90	11,111,111	788
100	10,000,000	876
200	5,000,000	1,752
300	3,333,333	2,628
400	2,500,000	3,504
500	2,000,000	4,380
600	1,666,667	5,256
700	1,428,571	6,132
800	1,250,000	7,008
900	1,111,111	7,884
1,000	1,000,000	8,760
2,000	500,000	17,520
3,000	333,333	26,280
4,000	250,000	35,040
5,000	200,000	43,800
6,000	166,667	52,560
7,000	142,857	61,320
8,000	125,000	70,080
9,000	111,111	78,840
10,000	100,000	87,600
20,000	50,000	175,200
30,000	33,333	262,800
40,000	25,000	350,400
50,000	20,000	438,000
60,000	16,667	525,600 ...