How to count the bits with a 1 bit error correction Hamming code? I've seen both ways of counting the bits when determining where to place the parity bits in a 1 bit error correction Hamming code. Some people count the bits starting from the left, others do it by starting from the right.

When to use one or the other? Does this depends on the Endian ordering?
Yes, it is about what bit-endianness you choose. Just make sure you are using the same interpretation on both ends.

(However if on 'Endian ordering' you meant byte order, that does not really apply here. As most Hamming codes do not transfer a whole number of data bytes, it is far simpler to think about the input as a stream of bits)