Introduction

The tables on this page were originally published in ELECTRONIC EXPERIMENTERS HANDBOOK, 1980, Page 70. The author is listed as R. E. MARTIN. I have adjusted the tables a bit, to make them easier to read. I also added the small calculator in the Optimum Q Inductors section. The calculator helps illustrate the formula given in the paragraph below it. Just enter your values and click anywhere on the page. - K7MEM

Optimum Q Inductors

Wire		Diameter & Length (inches)
AWG		1/8	1/4	3/8	1/2	5/8	3/4	1
16	T			6 Turns	8 Turns	10 Turns	12 Turns	16 Turns
	L*			0.233 µH	0..552 µH	1.08 µH	1.86 µH	4.41 µH
18	T		5 Turns	8 Turns	10-1/2 Turns	13 Turns	15-1/2 Turns	21 Turns
	L*		0.108 µH	0.414 µH	0.950 µH	1.82 µH	3.11 µH	7.60 µH
20	T	3 Turns	6-1/2 Turns	10 Turns	13 Turns	16-1/2 Turns	19-1/2 Turns	26 Turns
	L*	0.0194 µH	0.182 µH	0.647 µH	1.46 µH	2.93 µH	4.92 µH	11.7 µH
22	T	4 Turns	8 Turns	12 Turns	16-1/2 Turns	20 Turns	24-1/2 Turns	33 Turns
	L*	0.0345 µH	0.276 µH	0.931 µH	2.35 µH	4.31 µH	7.76 µH	18.8 µH
24	T	5 Turns	10 Turns	15 Turns	20-1/2 Turns	25 Turns	30-1/2 Turns	41 Turns
	L*	0.0539 µH	0.431 µH	1.46 µH	3.62 µH	6.74 µH	12.0 µH	29.0 µH
26	T	6-1/2 Turns	13 Turns	19-1/2 Turns	25-1/2 Turns	32-1/2 Turns	38-1/2 Turns	51 Turns
	L*	0.091 µH	0.728 µH	2.46 µH	5.61 µH	11.4 µH	19.2 µH	44.8 µH
28	T	8 Turns	16 Turns	24 Turns	32 Turns	40 Turns	48 Turns	64 Turns
	L*	0.138 µH	1.10 µH	3.72 µH	8.83 µH	17.2 µH	29.8 µH	70.6 µH
30	T	10 Turns	20 Turns	30 Turns	40 Turns	50 Turns	60 Turns	80 Turns
	L*	0.215 µH	1.72 µH	5.82 µH	13.8 µH	27.0 µH	46.5 µH	110 µH
	K	0.00215	0.00431	0.00647	0.00862	0.0108	0.0129	0.0172
*Inductance, L, is in microhenries

Calculate Inductance, L = K×T2
Number of Turns
K Value
Inductance (uH)	1.08 uH
Calculate Turns, T = √(L/K)
Inductance	µH
K Value
Number of Turns	10 Turns

Optimum Q is achieved in an inductor when its length and diameter are equal. This table will serve as a guide when designing high-Q inductors for R-F circuits. It gives maximum turns and inductance for various wire sizes when close-wound in a single layer.

Higher Q's will be obtained if the turns are spaced at one wire diameter. This results in half the turns and one quarter of the inductances listed in the table. Should an intermediate inductance or number of turns be desired, the factor, K, at the bottom of each column can be used for calculation from the formula L = K×T².

Small Inductors

Wire		Resistor Size				Wire		Resistor Size
AWG		1/4W	1/2W	1W	2W	AWG		1/4W	1/2W	1W	2W
20	T	3 Turns	7 Turns	11 Turns	14 Turns	30	T	9 Turns	19 Turns	32 Turns	41 Turns
	L*	0.013 µH	0.097 µH	0.32 µH	0.63 µH		L*	0.12 µH	0.72 µH	2.7 µH	5.4 µH
22	T	4 Turns	8 Turns	13 Turns	17 Turns	32	T	11 Turns	22 Turns	39 Turns	50 Turns
	L*	0.023 µH	0.13 µH	0.45 µH	0.92 µH		L*	0.12 µH	0.72 µH	2.7 µH	5.4 µH
24	T	5 Turns	10 Turns	17 Turns	22 Turns	34	T	14 Turns	28 Turns	49 Turns	62 Turns
	L*	0.036 µH	0.20 µH	0.76 µH	1.5 µH		L*	0.28 µH	1.6 µH	6.3 µH	12 µH
26	T	6 Turns	12 Turns	21 Turns	27 Turns	36	T	18 Turns	34 Turns	60 Turns	77 Turns
	L*	0.051 µH	0.29 µH	1.2 µH	2.3 µH		L*	0.46 µH	2.3 µH	9.5 µH	19 µH
28	T	8 Turns	15 Turns	26 Turns	33 Turns	*Inductance, L, is in microhenries
	L*	0.092 µH	0.45 µH	1.8 µH	3.5 µH

When small inductors are needed, for RF chokes or HF filter networks, it's frequently convenient to wind them on composition (carbon) resistors. The table shows inductances for various wire sizes when close-wound on common resistor bodies. The resistor value should be above 4.7 KΩ for the low-value inductances and above 47 KΩ for the higher values, unless low Q is desired.

The number of turns listed leaves a little space at the end of the resistor body to file small notches in order to guide the coil wire down to the resistor lead while not allowing the coil turns to fall off the ends. Do not use wire-wound resistors.