For polyhedra of side 1m, that "inradius" is

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```
tetrahedron 0.204124m
cube 0.500000m
octahedron 0.408248m
dodecahedron 1.113516m
icosahedron 0.755761m
```

So for a coil of 1m radius the equivalent "inradius" is

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```
tetrahedron 0.707106m
cube 1.000000m
octahedron 1.414213m
dodecahedron 1.618033m
icosahedron 2.618033m
```

For a Helmholtz coil of radius R, made of n turns of wire carrying a current I, the axial field B at distance x is

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```
mu_zero*n*I*R^2
B = -----------------
2*(R^2+x^2)^(3/2)
```

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```
tetrahedron 0.272166
cube 0.176777
octahedron 0.096225
dodecahedron 0.072654
icosahedron 0.022716
```

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```
tetrahedron 1.088663
cube 1.060660
octahedron 0.769801
dodecahedron 0.871852
icosahedron 0.454314
```