Harp strings are generally identified by their octave and pitch:

Middle C is the 4th octave C.
String Measurements
To work out which strings you need:
Nylon String Diameters
Pitch | Pedal Diamater (mm) | Lever Diamater (mm) |
Octave 0 | ||
G | 0.51 | - |
F | 0.51 | - |
1st Octave | ||
E | 0.54 | 0.51 |
D | 0.58 | 0.51 |
C | 0.60 | 0.54 |
B | 0.63 | 0.58 |
A | 0.66 | 0.58 |
G | 0.68 | 0.60 |
F | 0.71 | 0.63 |
2nd Octave | ||
E | 0.74 | 0.66 |
D | 0.76 | 0.68 |
C | 0.79 | 0.74 |
B | 0.82 | 0.74 |
A | 0.84 | 0.82 |
G | 0.88 | 0.84 |
F | 0.94 | 0.94 |
3rd Octave | ||
E | 0.99 | 0.94 |
D | 1.05 | 0.94 |
C | 1.10 | 1.05 |
B | 1.14 | 1.05 |
A | 1.18 | 1.05 |
G | 1.25 | 1.14 |
F | 1.32 | 1.18 |
4th Octave | ||
E | 1.36 | 1.18 |
D | 1.42 | 1.25 |
C | 1.47 | 1.32 |
B | 1.55 | 1.32 |
A | 1.67 | 1.36 |
G | 1.74 | 1.42 |
F | 1.81 | 1.42 |
Gut (Bow and Burgundy) String Diameters and Lengths
String number | Pitch | Pedal Diameter (mm) | Lever Diameter (mm) | Length (cm) |
1st Octave | ||||
1 | E | 0.56 | 0.47 | 122 |
2 | D | 0.58 | 0.50 | 122 |
3 | C | 0.60 | 0.52 | 122 |
4 | B | 0.62 | 0.54 | 122 |
5 | A | 0.64 | 0.56 | 122 |
6 | G | 0.66 | 0.58 | 122 |
7 | F | 0.68 | 0.60 | 122 |
2nd Octave | ||||
8 | E | 0.70 | 0.62 | 122 |
9 | D | 0.73 | 0.64 | 122 |
10 | C | 0.76 | 0.66 | 122 |
11 | B | 0.80 | 0.68 | 122 |
12 | A | 0.85 | 0.70 | 122 |
13 | G | 0.88 | 0.73 | 122 |
14 | F | 0.92 | 0.76 | 122 |
3rd Octave | ||||
15 | E | 0.95 | 0.80 | 122 (lever), 152 (pedal) |
16 | D | 1.00 | 0.85 | 122 (lever), 152 (pedal) |
17 | C | 1.05 | 0.90 | 122 (lever), 152 (pedal) |
18 | B | 1.10 | 0.95 | 122 (lever), 152 (pedal) |
19 | A | 1.15 | 1.00 | 122 (lever), 152 (pedal) |
20 | G | 1.20 | 1.05 | 122 (lever), 152 (pedal) |
21 | F | 1.25 | 1.10 | 122 (lever), 152 (pedal) |
4th Octave | ||||
22 | E | 1.30 | 1.15 | 122 |
23 | D | 1.35 | 1.20 | 122 |
24 | C | 1.45 | 1.25 | 122 |
25 | B | 1.55 | 1.30 | 122 |
26 | A | 1.60 | 1.36 | 122 |
27 | G | 1.70 | 1.44 | 122 |
28 | F | 1.80 | 1.52 | 122 |
5th Octave | ||||
29 | E | 1.85 | 1.60 | 152 |
30 | D | 1.96 | 1.70 | 152 |
31 | C | 2.08 | 1.80 | 152 |
32 | B | 2.18 | 1.90 | 152 |
33 | A | 2.29 | 2.00 | 152 |
34 | G | 2.35 | 2.10 | 152 |
35 | F | 2.50 | 2.20 | 152 |
Pedal Harp Bass Wire Diameters and Lengths
String number | Pitch | Diameter (mm) | Length (cm) |
5th Octave | |||
33 | A | 1.60 | 145 |
34 | G | 1.65 | 150 |
35 | F | 1.70 | 150 |
6th Octave | |||
36 | E | 1.80 | 155 |
37 | D | 1.90 | 160 |
38 | C | 2.00 | 165 |
39 | B | 2.10 | 165 |
40 | A | 2.25 | 170 |
41 | G | 2.45 | 175 |
42 | F | 2.50 | 180 |
7th Octave | |||
43 | E | 2.70 | 180 |
44 | D | 2.80 | 185 |
45 | C | 2.85 | 185 |
Lever Harp Bass Wire Diameters and Lengths
String number | Pitch | Diameter (mm) | Length (cm) |
5th Octave | |||
29 | E | 1.25 | 110 |
30 | D | 1.29 | 110 |
31 | C | 1.35 | 120 |
32 | B | 1.44 | 120 |
33 | A | 1.47 | 125 |
34 | G | 1.50 | 135 |
35 | F | 1.55 | 140 |
6th Octave | |||
36 | E | 1.60 | 145 |
37 | D | 1.67 | 150 |
38 | C | 1.76 | 155 |
39 | B | 1.87 | 155 |
40 | A | 1.97 | 155 |