Calculating inductance for standard size toroids uses simple formulas. I keep needing the same information so here is a table of useful values (inductances in microhenries):
Toroid | T37-2 | T50-2 | T68-2 | T37-6 | T50-6 | T68-6 | T37-10 | T50-10 | |
Number of turns | Al (nH/N2) | 4 | 4.9 | 5.7 | 3 | 4 | 4.7 | 2.5 | 3.1 |
1 | 0.004 | 0.0049 | 0.0057 | 0.003 | 0.004 | 0.0047 | 0.0025 | 0.0031 | |
2 | 0.016 | 0.0196 | 0.0228 | 0.012 | 0.016 | 0.0188 | 0.01 | 0.0124 | |
3 | 0.036 | 0.0441 | 0.0513 | 0.027 | 0.036 | 0.0423 | 0.0225 | 0.0279 | |
4 | 0.064 | 0.0784 | 0.0912 | 0.048 | 0.064 | 0.0752 | 0.04 | 0.0496 | |
5 | 0.1 | 0.1225 | 0.1425 | 0.075 | 0.1 | 0.1175 | 0.0625 | 0.0775 | |
6 | 0.144 | 0.1764 | 0.2052 | 0.108 | 0.144 | 0.1692 | 0.09 | 0.1116 | |
7 | 0.196 | 0.2401 | 0.2793 | 0.147 | 0.196 | 0.2303 | 0.1225 | 0.1519 | |
8 | 0.256 | 0.3136 | 0.3648 | 0.192 | 0.256 | 0.3008 | 0.16 | 0.1984 | |
9 | 0.324 | 0.3969 | 0.4617 | 0.243 | 0.324 | 0.3807 | 0.2025 | 0.2511 | |
10 | 0.4 | 0.49 | 0.57 | 0.3 | 0.4 | 0.47 | 0.25 | 0.31 | |
11 | 0.484 | 0.5929 | 0.6897 | 0.363 | 0.484 | 0.5687 | 0.3025 | 0.3751 | |
12 | 0.576 | 0.7056 | 0.8208 | 0.432 | 0.576 | 0.6768 | 0.36 | 0.4464 | |
13 | 0.676 | 0.8281 | 0.9633 | 0.507 | 0.676 | 0.7943 | 0.4225 | 0.5239 | |
14 | 0.784 | 0.9604 | 1.1172 | 0.588 | 0.784 | 0.9212 | 0.49 | 0.6076 | |
15 | 0.9 | 1.1025 | 1.2825 | 0.675 | 0.9 | 1.0575 | 0.5625 | 0.6975 | |
16 | 1.024 | 1.2544 | 1.4592 | 0.768 | 1.024 | 1.2032 | 0.64 | 0.7936 | |
17 | 1.156 | 1.4161 | 1.6473 | 0.867 | 1.156 | 1.3583 | 0.7225 | 0.8959 | |
18 | 1.296 | 1.5876 | 1.8468 | 0.972 | 1.296 | 1.5228 | 0.81 | 1.0044 | |
19 | 1.444 | 1.7689 | 2.0577 | 1.083 | 1.444 | 1.6967 | 0.9025 | 1.1191 | |
20 | 1.6 | 1.96 | 2.28 | 1.2 | 1.6 | 1.88 | 1 | 1.24 | |
21 | 1.764 | 2.1609 | 2.5137 | 1.323 | 1.764 | 2.0727 | 1.1025 | 1.3671 | |
22 | 1.936 | 2.3716 | 2.7588 | 1.452 | 1.936 | 2.2748 | 1.21 | 1.5004 | |
23 | 2.116 | 2.5921 | 3.0153 | 1.587 | 2.116 | 2.4863 | 1.3225 | 1.6399 | |
24 | 2.304 | 2.8224 | 3.2832 | 1.728 | 2.304 | 2.7072 | 1.44 | 1.7856 | |
25 | 2.5 | 3.0625 | 3.5625 | 1.875 | 2.5 | 2.9375 | 1.5625 | 1.9375 | |
26 | 2.704 | 3.3124 | 3.8532 | 2.028 | 2.704 | 3.1772 | 1.69 | 2.0956 | |
27 | 2.916 | 3.5721 | 4.1553 | 2.187 | 2.916 | 3.4263 | 1.8225 | 2.2599 | |
28 | 3.136 | 3.8416 | 4.4688 | 2.352 | 3.136 | 3.6848 | 1.96 | 2.4304 | |
29 | 3.364 | 4.1209 | 4.7937 | 2.523 | 3.364 | 3.9527 | 2.1025 | 2.6071 | |
30 | 3.6 | 4.41 | 5.13 | 2.7 | 3.6 | 4.23 | 2.25 | 2.79 | |
31 | 3.844 | 4.7089 | 5.4777 | 2.883 | 3.844 | 4.5167 | 2.4025 | 2.9791 | |
32 | 4.096 | 5.0176 | 5.8368 | 3.072 | 4.096 | 4.8128 | 2.56 | 3.1744 | |
33 | 4.356 | 5.3361 | 6.2073 | 3.267 | 4.356 | 5.1183 | 2.7225 | 3.3759 | |
34 | 4.624 | 5.6644 | 6.5892 | 3.468 | 4.624 | 5.4332 | 2.89 | 3.5836 | |
35 | 4.9 | 6.0025 | 6.9825 | 3.675 | 4.9 | 5.7575 | 3.0625 | 3.7975 |