now, do you trust the coin? Maybe your coin has a bias to land on head, because of uneven weight distribution. A bias can have a negative effect on the entropy of the bits produced. studies say average coin bias is 51/49, which is low enough to not be an issue. If you still don't trust the coin, you can use von neumann normalization. For each throw, you do 2 throws instead: if heads, heads => rethrow tails, tails => rethrow heads,tails => heads tails, head => tails this will require more than double the throws, but will give you unbiased entropy