ikegami,

I can see how that would tell you where the white queen is located, but how can you tell where the black queen is located with that? Aren't you missing the 6 bytes for black?

Indeed. It was 4 in the morning and I was thinking there were only 8 pieces on each side - 16 * 3 = 48, 48 / 8 = 6.

You can save a byte by using a variable base number.

I actually had more efficient storage solutions (more than 23 bytes but less than 29) that were probably correct but I have given up at this point - sleep comes for us all eventually.