Antenna Length Calculator
Antenna Length Calculator
Frequency: MHz Type: Diameter:
Velocity of light (ISO 1992 standard) (V) = 299,792,458 meters per second
Frequency (F) = 21.000 MHz ( 14 m band)
1/2 Wavelength in free space = ( V(km)/F(kHz)/2 ) = 23' 5" | 7.138 m
Minimum recommended height (1/4 wavelength) = 11' 8-1/2" | 3.569 m
Wire Antenna Element Data: ( AWG# 14 )
Antenna element diameter = 0.064" | 1.628 mm
Ratio of 1/2 wavelength to element diameter = 4,385.205:1
Velocity factor of conductor (approximate)(K) = 0.98
Wire Antenna Element Lengths: *ALK (Length = ALK ÷ Frequency in MHz)
1/2 λ Flat Top (e.g. Dipole): 467.2 | 142.4 22' 3" | 6.781 m
1/4 λ Vertical (height) 234.0 | 71.3 11' 1-3/4" | 3.396 m
1/2 λ End Fed, Single Wire 467.2 | 142.4 22' 3" | 6.781 m
1 λ End Fed, Single Wire 959.0 | 292.3 45' 8" | 13.919 m
3/2 λ End Fed, Single Wire 1450.8 | 442.2 69' 1" | 21.057 m
2 λ End Fed, Single Wire 1942.6 | 592.1 92' 6" | 28.195 m
*ALK = Antenna Length Constant. Includes calculated K and end-effect factors.

This calculator is an aid for determining antenna element lengths, based on Frequency, Type (Wire or Tubing), and Diameter (AWG#, inches, mm) of the element.

At the top of the calculator, enter the Frequency (1 to 30 MHz) of interest. You can enter any frequency you like, however, the tables are only valid for 1 to 30 MHz. If you enter data outside this range, the value in the entry area will be adjusted. Then enter the Type and Diameter of your antenna element. When using Tubing, the diameter entered should be the outside diameter of the tubing.

The calculator first computes the antenna length (1/2 Wavelength) and recommended height (1/4 Wavelength) above ground, for an antenna in Free Space. The calculator then determines the Length/Diameter Ratio and the approximate Velocity Factor. The Velocity Factor is then used to calculate the Antenna Length Constant (ALK), which includes calculated K and end-effect factors. When the ALK is divided by the Frequency (MHz), the adjusted length is produced.

The botton two sections of the calculator list the ALK and element lengths for 1/2 λ Dipole, 1/4 λ Vertical, and 1/2 λ, 1 λ, 3/2 λ, and 2 λ Single Wire End Fed lengths. Output data is in US/Imperial and Metric formats.

Table of Horizontal Antenna Lengths from 1 to 7 Half-Wavelengths

This section contains three tables that can calculate antenna shortening factors and antenna lengths, including quarter-wave verticals over perfect ground, half-wavelength dipoles in free space, and long wire vertical and horizontal antennas. Just enter your frequency of interest in the space provided. While you can enter any frequency you like, the tables are only valid for 3 to 30 MHz. Output data is in US/Imperial and Metric formats. All dimensions are calibrated to NEC-2 antenna models.

Programmed materials are AWG #18 (1.0 mm) to AWG #10 (2.6 mm) copper wire, and aluminum rod or tubing from 0.125" (3.2 mm) to 2" (50.8 mm) diameter.

Table of Horizontal Antenna Lengths from 1 to 7 Half-Wavelengths
AWG Wire sizes are copper. Other conductor sizes are aluminum.
Frequency: MHz Wavelength in Free Space = 46' 10" | 14.276 m
¦———— Wire Size ————¦ Lengths, in Feet | Meters, for N number of ½-wavelengths
   AWGN=1 N=2N=3 N=4N=5 N=6N=7
#18 - 0.0403" =  1.0 mm 22' 8-3/4"
6.928 m
46' 1-1/2"
14.057 m
69' 6"
21.185 m
92' 10-3/4"
28.314 m
116' 3-1/4"
35.442 m
139' 8"
42.571 m
163' 0-3/4"
49.699 m
#16 - 0.0508" =  1.3 mm 22' 8-1/2"
6.923 m
46' 1-1/4"
14.053 m
69' 6"
21.182 m
92' 10-3/4"
28.312 m
116' 3-1/4"
35.442 m
139' 8"
42.571 m
163' 0-3/4"
49.701 m
#14 - 0.0641" =  1.6 mm 22' 8-1/4"
6.917 m
46' 1"
14.048 m
69' 5-3/4"
21.178 m
92' 10-1/2"
28.309 m
116' 3-1/4"
35.44 m
139' 8"
42.57 m
163' 0-3/4"
49.701 m
#12 - 0.0808" =  2.1 mm 22' 8"
6.911 m
46' 0-3/4"
14.042 m
69' 5-1/2"
21.173 m
92' 10-1/4"
28.304 m
116' 3"
35.436 m
139' 7-3/4"
42.567 m
163' 0-3/4"
49.698 m
#10 - 0.1019" =  2.6 mm 22' 7-3/4"
6.903 m
46' 0-1/2"
14.035 m
69' 5-1/4"
21.167 m
92' 10"
28.299 m
116' 3"
35.431 m
139' 7-3/4"
42.562 m
163' 0-1/2"
49.694 m
0.125" =  3.2 mm 22' 7-1/2"
6.895 m
46' 0-1/4"
14.026 m
69' 5"
21.157 m
92' 9-3/4"
28.288 m
116' 2-1/2"
35.42 m
139' 7-1/4"
42.551 m
162' 12"
49.682 m
0.250" =  6.4 mm 22' 6-1/4"
6.866 m
45' 11-1/4"
13.999 m
69' 4"
21.131 m
92' 8-3/4"
28.264 m
116' 1-1/2"
35.396 m
139' 6-1/4"
42.529 m
162' 11-1/4"
49.662 m
0.500" = 12.7 mm 22' 4-3/4"
6.827 m
45' 9-3/4"
13.961 m
69' 2-1/2"
21.095 m
92' 7-1/4"
28.228 m
116' 0-1/4"
35.362 m
139' 5"
42.496 m
162' 10"
49.63 m
0.750" = 19.0 mm 22' 3-3/4"
6.798 m
45' 8-1/2"
13.933 m
69' 1-1/2"
21.067 m
92' 6-1/4"
28.201 m
115' 11-1/4"
35.336 m
139' 4"
42.47 m
162' 9"
49.604 m
1.000" = 25.4 mm 22' 2-3/4"
6.775 m
45' 7-1/2"
13.91 m
69' 0-1/2"
21.045 m
92' 5-1/2"
28.179 m
115' 10-1/4"
35.314 m
139' 3-1/4"
42.449 m
162' 8-1/4"
49.584 m
1.250" = 31.8 mm 22' 2"
6.754 m
45' 6-3/4"
13.89 m
68' 11-3/4"
21.025 m
92' 4-3/4"
28.161 m
115' 9-1/2"
35.296 m
139' 2-1/2"
42.432 m
162' 7-1/2"
49.567 m
1.500" = 38.1 mm 22' 1-1/4"
6.737 m
45' 6-1/4"
13.873 m
68' 11"
21.009 m
92' 4"
28.145 m
115' 9"
35.281 m
139' 2"
42.417 m
162' 7"
49.553 m
1.750" = 44.5 mm 22' 0-1/2"
6.721 m
45' 5-1/2"
13.857 m
68' 10-1/2"
20.994 m
92' 3-1/2"
28.131 m
115' 8-1/2"
35.267 m
139' 1-1/2"
42.404 m
162' 6-1/2"
49.541 m
2.000" = 50.8 mm 22' 0"
6.706 m
45' 5"
13.844 m
68' 10"
20.981 m
92' 3"
28.118 m
115' 8"
35.256 m
139' 1"
42.393 m
162' 6"
49.53 m
Table of Vertical Antenna Lengths from 1 to 7 Quarter-Wavelengths
Table of Vertical Antenna Lengths from 1 to 7 Quarter-Wavelengths
AWG Wire sizes are copper. Other conductor sizes are aluminum.
Vertical antennas assumed to be over perfect ground.
Frequency: MHz Wavelength in Free Space = 46' 10" | 14.276 m
¦———— Wire Size ————¦ Lengths, in Feet/Meters, for N number of ¼-wavelengths
   AWGN=1 N=2N=3 N=4N=5 N=6N=7
#18 - 0.0403" =  1.0 mm 11' 4-1/2"
3.464 m
23' 0-3/4"
7.028 m
34' 9"
10.593 m
46' 5-1/4"
14.157 m
58' 1-3/4"
17.721 m
69' 10"
21.285 m
81' 6-1/4"
24.85 m
#16 - 0.0508" =  1.3 mm 11' 4-1/4"
3.462 m
23' 0-3/4"
7.026 m
34' 9"
10.591 m
46' 5-1/4"
14.156 m
58' 1-3/4"
17.721 m
69' 10"
21.286 m
81' 6-1/4"
24.85 m
#14 - 0.0641" =  1.6 mm 11' 4-1/4"
3.459 m
23' 0-1/2"
7.024 m
34' 9"
10.589 m
46' 5-1/4"
14.155 m
58' 1-3/4"
17.72 m
69' 10"
21.285 m
81' 6-1/4"
24.85 m
#12 - 0.0808" =  2.1 mm 11' 4"
3.455 m
23' 0-1/2"
7.021 m
34' 8-3/4"
10.587 m
46' 5-1/4"
14.152 m
58' 1-1/2"
17.718 m
69' 10"
21.284 m
81' 6-1/4"
24.849 m
#10 - 0.1019" =  2.6 mm 11' 4"
3.452 m
23' 0-1/4"
7.018 m
34' 8-3/4"
10.583 m
46' 5"
14.149 m
58' 1-1/2"
17.715 m
69' 9-3/4"
21.281 m
81' 6-1/4"
24.847 m
0.125" =  3.2 mm 11' 3-3/4"
3.447 m
23' 0"
7.013 m
34' 8-1/2"
10.579 m
46' 4-3/4"
14.144 m
58' 1-1/4"
17.71 m
69' 9-1/2"
21.275 m
81' 6"
24.841 m
0.250" =  6.4 mm 11' 3-1/4"
3.433 m
22' 11-1/2"
6.999 m
34' 8"
10.566 m
46' 4-1/2"
14.132 m
58' 0-3/4"
17.698 m
69' 9-1/4"
21.265 m
81' 5-1/2"
24.831 m
0.500" = 12.7 mm 11' 2-1/2"
3.414 m
22' 10-3/4"
6.98 m
34' 7-1/4"
10.547 m
46' 3-3/4"
14.114 m
58' 0"
17.681 m
69' 8-1/2"
21.248 m
81' 5"
24.815 m
0.750" = 19.0 mm 11' 1-3/4"
3.399 m
22' 10-1/4"
6.966 m
34' 6-3/4"
10.533 m
46' 3-1/4"
14.101 m
57' 11-1/2"
17.668 m
69' 8"
21.235 m
81' 4-1/2"
24.802 m
1.000" = 25.4 mm 11' 1-1/4"
3.387 m
22' 9-3/4"
6.955 m
34' 6-1/4"
10.522 m
46' 2-3/4"
14.09 m
57' 11-1/4"
17.657 m
69' 7-1/2"
21.225 m
81' 4"
24.792 m
1.250" = 31.8 mm 11' 1"
3.377 m
22' 9-1/2"
6.945 m
34' 6"
10.513 m
46' 2-1/4"
14.08 m
57' 10-3/4"
17.648 m
69' 7-1/4"
21.216 m
81' 3-3/4"
24.784 m
1.500" = 38.1 mm 11' 0-1/2"
3.368 m
22' 9"
6.936 m
34' 5-1/2"
10.504 m
46' 2"
14.072 m
57' 10-1/2"
17.64 m
69' 7"
21.208 m
81' 3-1/2"
24.776 m
1.750" = 44.5 mm 11' 0-1/4"
3.36 m
22' 8-3/4"
6.929 m
34' 5-1/4"
10.497 m
46' 1-3/4"
14.065 m
57' 10-1/4"
17.634 m
69' 6-3/4"
21.202 m
81' 3-1/4"
24.77 m
2.000" = 50.8 mm 11' 0"
3.353 m
22' 8-1/2"
6.922 m
34' 5"
10.491 m
46' 1-1/2"
14.059 m
57' 10"
17.628 m
69' 6-1/2"
21.197 m
81' 3"
24.765 m
Calculation of K, the Antenna Shortening Factor
Calculation of K, the Antenna Shortening Factor
KT is the total shortening factor. KM is the shortening factor due to element
material. KE is the shortening factor due to end effect. Values calibrated to
NEC-2 models for 3-30 MHz. AWG sizes are copper. Other sizes are aluminum.
Frequency: MHz Wavelength in Free Space = 46' 10" | 14.276 m
¦———— Wire Size ————¦ ¼-wave Vertical½-wave Dipole
   AWG KT KM KE Length Length
#18 - 0.0403" =  1.0 mm 0.9706 0.9987 0.9719 11' 4-1/2" | 3.4642 m 22' 8-3/4" | 6.9284 m
#16 - 0.0508" =  1.3 mm 0.9699 0.9988 0.9711 11' 4-1/4" | 3.4616 m 22' 8-1/2" | 6.9233 m
#14 - 0.0641" =  1.6 mm 0.9691 0.9990 0.9701 11' 4-1/4" | 3.4586 m 22' 8-1/4" | 6.9172 m
#12 - 0.0808" =  2.1 mm 0.9682 0.9991 0.9691 11' 4" | 3.4553 m 22' 8" | 6.9106 m
#10 - 0.1019" =  2.6 mm 0.9671 0.9992 0.9679 11' 4" | 3.4516 m 22' 7-3/4" | 6.9032 m
0.125" =  3.2 mm 0.9660 0.9991 0.9669 11' 3-3/4" | 3.4475 m 22' 7-1/2" | 6.8950 m
0.250" =  6.4 mm 0.9619 0.9993 0.9626 11' 3-1/4" | 3.4331 m 22' 6-1/4" | 6.8661 m
0.500" = 12.7 mm 0.9565 0.9994 0.9570 11' 2-1/2" | 3.4136 m 22' 4-3/4" | 6.8273 m
0.750" = 19.0 mm 0.9524 0.9995 0.9529 11' 1-3/4" | 3.3992 m 22' 3-3/4" | 6.7984 m
1.000" = 25.4 mm 0.9491 0.9996 0.9495 11' 1-1/4" | 3.3874 m 22' 2-3/4" | 6.7748 m
1.250" = 31.8 mm 0.9463 0.9997 0.9466 11' 1" | 3.3772 m 22' 2" | 6.7545 m
1.500" = 38.1 mm 0.9438 0.9997 0.9440 11' 0-1/2" | 3.3684 m 22' 1-1/4" | 6.7367 m
1.750" = 44.5 mm 0.9416 0.9998 0.9417 11' 0-1/4" | 3.3604 m 22' 0-1/2" | 6.7207 m
2.000" = 50.8 mm 0.9396 0.9999 0.9396 11' 0" | 3.3532 m 22' 0" | 6.7065 m