One-Sentence Definition
Joules per terahash (J/TH) measures how much energy a mining device uses to produce one terahash of computing power, with lower numbers meaning better efficiency.
Why It Matters for Solo Mining
When you’re solo mining, you might be running hardware for months without finding a block, so energy efficiency directly impacts how much you spend waiting for that lucky moment. A miner using 30 J/TH costs half as much to run as one using 60 J/TH with the same hashrate, which dramatically affects your mining profitability when dealing with the high variance of solo mining. Since your electricity cost per kWh keeps ticking whether you find a block or not, choosing efficient hardware is crucial for staying in the game long enough to hit that solo block.
How It Works
The J/TH rating tells you exactly how many joules (units of energy) your miner burns through for every trillion hashes it computes. To calculate it, you divide the miner’s power consumption in watts by its hashrate in terahashes per second—for example, a 3000-watt miner running at 100 TH/s uses 30 J/TH. Modern ASIC miners have gotten way more efficient over the years, dropping from 100+ J/TH in early models to under 20 J/TH in current generation hardware.
This metric matters more than raw power consumption because it accounts for how much work you’re getting done per unit of energy. Your power supply unit needs to handle the total wattage, but J/TH tells you if you’re getting good value from that electricity. Keep in mind that efficiency can drop if your miner experiences thermal throttling from inadequate cooling.
Example
The Antminer S19 XP uses about 3010 watts to produce 140 TH/s, which works out to roughly 21.5 J/TH. Compare that to an older S9 that uses 1350 watts for 13.5 TH/s—that’s 100 J/TH, nearly five times less efficient! If you’re solo mining Bitcoin and your expected time to block is six months, the S19 XP would cost you about $900 in electricity at $0.12/kWh, while the S9 would cost you roughly $583 but give you way less chance of actually finding a block due to lower hashrate.