How many small bale of hay in a 3x3x8 square bale?

Depends on the weight of the bales (both the small squares and large round) and whether that bale is comprised of hay or straw. All bales of hay, straw or baleage are sold in terms of weight (in tons or pounds), not size. Not all LRB's are going to be 5x5; a lot of them range from 4x5 to 6x6. And even then it also depends on how densely packed they are, which ultimately affects their weight.

However, let's assume your asking about a 5x5 1500 lb LRB and wondering how many SSBs (assuming they are around 75 lbs each) fit into that particular bale or bales with that similar weight. So, 1500 / 75 = 20 bales; thus it is estimated that 20 SSBs will fit into one 5x5 LRB assuming the weights are what they are.