It is possible to use a 3x3 magic square and a 4x4 magic square to construct a 12x12 magic square.
Use as first grid 4x4 the same 3x3 magic square and as second grid 3x3 the same 4x4 magic square. Take a number from a cell of the first grid and add (number -/- 1) x 9 from the same cell of the second grid.
1x number
2 | 9 | 4 | 2 | 9 | 4 | 2 | 9 | 4 | 2 | 9 | 4 |
7 | 5 | 3 | 7 | 5 | 3 | 7 | 5 | 3 | 7 | 5 | 3 |
6 | 1 | 8 | 6 | 1 | 8 | 6 | 1 | 8 | 6 | 1 | 8 |
2 | 9 | 4 | 2 | 9 | 4 | 2 | 9 | 4 | 2 | 9 | 4 |
7 | 5 | 3 | 7 | 5 | 3 | 7 | 5 | 3 | 7 | 5 | 3 |
6 | 1 | 8 | 6 | 1 | 8 | 6 | 1 | 8 | 6 | 1 | 8 |
2 | 9 | 4 | 2 | 9 | 4 | 2 | 9 | 4 | 2 | 9 | 4 |
7 | 5 | 3 | 7 | 5 | 3 | 7 | 5 | 3 | 7 | 5 | 3 |
6 | 1 | 8 | 6 | 1 | 8 | 6 | 1 | 8 | 6 | 1 | 8 |
2 | 9 | 4 | 2 | 9 | 4 | 2 | 9 | 4 | 2 | 9 | 4 |
7 | 5 | 3 | 7 | 5 | 3 | 7 | 5 | 3 | 7 | 5 | 3 |
6 | 1 | 8 | 6 | 1 | 8 | 6 | 1 | 8 | 6 | 1 | 8 |
+ (number -/- 1) x 9
1 | 8 | 13 | 12 | 1 | 8 | 13 | 12 | 1 | 8 | 13 | 12 |
15 | 10 | 3 | 6 | 15 | 10 | 3 | 6 | 15 | 10 | 3 | 6 |
4 | 5 | 16 | 9 | 4 | 5 | 16 | 9 | 4 | 5 | 16 | 9 |
14 | 11 | 2 | 7 | 14 | 11 | 2 | 7 | 14 | 11 | 2 | 7 |
1 | 8 | 13 | 12 | 1 | 8 | 13 | 12 | 1 | 8 | 13 | 12 |
15 | 10 | 3 | 6 | 15 | 10 | 3 | 6 | 15 | 10 | 3 | 6 |
4 | 5 | 16 | 9 | 4 | 5 | 16 | 9 | 4 | 5 | 16 | 9 |
14 | 11 | 2 | 7 | 14 | 11 | 2 | 7 | 14 | 11 | 2 | 7 |
1 | 8 | 13 | 12 | 1 | 8 | 13 | 12 | 1 | 8 | 13 | 12 |
15 | 10 | 3 | 6 | 15 | 10 | 3 | 6 | 15 | 10 | 3 | 6 |
4 | 5 | 16 | 9 | 4 | 5 | 16 | 9 | 4 | 5 | 16 | 9 |
14 | 11 | 2 | 7 | 14 | 11 | 2 | 7 | 14 | 11 | 2 | 7 |
= composite magic 12x12 square
2 | 72 | 112 | 101 | 9 | 67 | 110 | 108 | 4 | 65 | 117 | 103 |
133 | 86 | 21 | 52 | 131 | 84 | 25 | 50 | 129 | 88 | 23 | 48 |
33 | 37 | 143 | 78 | 28 | 44 | 141 | 73 | 35 | 42 | 136 | 80 |
119 | 99 | 13 | 56 | 126 | 94 | 11 | 63 | 121 | 92 | 18 | 58 |
7 | 68 | 111 | 106 | 5 | 66 | 115 | 104 | 3 | 70 | 113 | 102 |
132 | 82 | 26 | 51 | 127 | 89 | 24 | 46 | 134 | 87 | 19 | 53 |
29 | 45 | 139 | 74 | 36 | 40 | 137 | 81 | 31 | 38 | 144 | 76 |
124 | 95 | 12 | 61 | 122 | 93 | 16 | 59 | 120 | 97 | 14 | 57 |
6 | 64 | 116 | 105 | 1 | 71 | 114 | 100 | 8 | 69 | 109 | 107 |
128 | 90 | 22 | 47 | 135 | 85 | 20 | 54 | 130 | 83 | 27 | 49 |
34 | 41 | 138 | 79 | 32 | 39 | 142 | 77 | 30 | 43 | 140 | 75 |
123 | 91 | 17 | 60 | 118 | 98 | 15 | 55 | 125 | 96 | 10 | 62 |
This composite magic 12x12 square has as extra feature that each random chosen 3x4 or 4x3 rectangle inside the square gives the magic sum of 870.
I have used the method composite, AxB compact to construct
12x12, 15x15, 20x20, 21x21, 24x24, 28x28, 30x30a and 30x30b