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