Definition
J/TH — joules per terahash — is the standard efficiency metric for Bitcoin ASIC miners. It expresses how much energy a machine burns to perform one terahash (10¹² hashes) of work. Because a watt is one joule per second, you can read J/TH directly as the miner's wall power in watts divided by its hashrate in TH/s. The lower the number, the more efficient the miner, and the cheaper each unit of hashrate is to run.
Why it's the number that matters
Two miners can have the same hashrate but very different electricity bills; J/TH is what tells them apart. In a market where power is the dominant ongoing cost, efficiency is the difference between profit and loss — which is why miners chase low-J/TH hardware and use autotuning firmware to shave the number further.
Generational context
The jump between generations is large. An Antminer S19 Pro runs around 29.5 J/TH at stock, while the S21 family lands near 17.5 J/TH and the S21 XP reaches roughly 13.5 J/TH — making the newest flagships nearly twice as efficient as a four-year-old machine. That gap is exactly why old miners get curtailed first when electricity prices rise.
Compare current models on our live ASIC efficiency frontier, or see practical tuning in the S19 power-efficiency guide.
In Simple Terms
J/TH — joules per terahash — is the standard efficiency metric for Bitcoin ASIC miners. It expresses how much energy a machine burns to perform…