Resistors in parallel

- The values produced by placing resistors in parallel including a reference table

When designing or building an electronic circuit, it may be necessary to use two or more resistors instead of one. Either the correct value of resistor may not be available, or it may be necessary to dissipate a higher power than that which a single resistor can dissipate on its own.

Resistance of resistor combinations
Resistors can be placed in series or parallel. When placed in series the total resistance is equal to the sum of the individual resistors:

Resistors in series

It is also worth noting that the same current flows through each resistor, but the voltage across each resistor is proportional to the resistance of that particular resistor.

For resistors placed in parallel, the arithmetic is a little more complicated because the reciprocal of the total resistance is equal to the sum of the reciprocals of the constituent resistors:

Resistors in parallel

When there are only two resistors R1 and R2 in parallel this can be simplified to:

Parallel resistor value table
While the values for resistors in parallel can be calculated relatively easily in most cases a table giving suitable values that are in the most case preferred is given below. Column A gives the required resistor value, and column B gives the first choice combination for the parallel resistors. A second choice is shown in column C. The values should be a close tolerance as possible, typically 0.5%.

Required resistor value "A"	First selection of resistors "B"		Alternative selection of resistors "C"
10.0	10		11	110
11.0	11		12	130
12.0	12		13	150
13.0	13		15	100
14.0	16	110	15	220
15.0	15		16	240
16.0	16		27	39
17.0	22	75	18	300
18.0	18		20	180
19.0	24	91	20	390
20.0	20		22	220
22.0	22		24	270
23.0	39	56	24	560
24.0	24		27	220
25.0	30	150	27	330
26.0	27	680	30	200
27.0	27		30	270
28.0	51	62	30	430
29.0	33	240	30	910
30.0	30		33	330
31.0	33	510	39	150
32.0	47	100	33	1100
33.0	33		36	390
34.0	68	68	162	75
35.0	36	1200	39	330
36.0	36		39	470
37.0	39	750	43	270
38.0	39	1500	43	330
39.0	39		68	91
40.0	47	270	43	560
41.0	82	82	43	910
42.0	43	1800	62	130
43.0	43		47	510
44.0	47	680	62	150
45.0	82	100	47	1100
46.0	47	2200	51	470
47.0	47		82	110
48.0	51	820	56	330
49.0	56	390	51	1300
50.0	75	150	56	470
51.0	51		56	560
52.0	68	220	56	750
53.0	68	240	56	1000
54.0	56	1500	62	430
55.0	110	110	56	3000
56.0	56		75	220
57.0	75	240	62	680
58.0	91	160	62	910
59.0	62	1200	62	1300
60.0	68	510	75	300
62.0	62		75	360
64.0	68	1100	75	430
66.0	91	240	68	2200
68.0	68		91	270
70.0	82	470	75	1000
72.0	75	1800	120	180
74.0	75	5600	82	750
76.0	82	1000	91	470
78.0	62	1600	110	270
80.0	120	240	82	3300
82.0	82		91	620
84.0	91	1100	110	360
86.0	100	620	91	1500
88.0	120	330	91	2700
90.0	120	360	91	8200
92.0	110	560	120	390
94.0	100	1600	120	430
96.0	100	2400	110	750
98.0	100	5100	110	910