Efficiency (J/TH)

Efficiency determines operating cost per unit of revenue. An Antminer S21 XP at ~12 J/TH spends roughly half the electricity per terahash of an S19k Pro at ~23 J/TH — meaning it stays profitable at electricity prices that bankrupt the older unit. Equivalent metrics exist per algorithm: J/MH for Scrypt and Etchash, J/GH elsewhere.

As difficulty rises and rewards halve, the network's average efficiency improves and the break-even bar rises with it. A useful rule: buy the best efficiency you can afford, not the most hashrate — hashrate determines how much you earn, efficiency determines whether you profit.