Energy efficiency
Also called: J/TH, J/GH, J/MH, power efficiency
A miner's energy efficiency shows the energy used per unit of hashrate, in J/TH or J/GH. The lower the figure, the more efficient the machine.
Energy efficiency compares what a machine consumes with what it produces. It is expressed in joules per terahash (J/TH) for SHA-256, in joules per gigahash (J/GH) for Scrypt, or in J/MH and J/kSol depending on the algorithm. Since one joule per second is one watt, the calculation is simple: divide the power in watts by the hashrate.
Take a fictitious example: a machine drawing 3,500 W for 200 TH/s comes in at 17.5 J/TH. Another drawing 3,500 W for 250 TH/s drops to 14 J/TH: for the same electricity bill, it produces a quarter more hashrate. This is why efficiency determines a machine's economic lifespan, especially after a halving or a rise in difficulty.
On a product page, efficiency is often stated for an ambient temperature of around 25 °C, with a tolerance. It gets worse when the machine runs hot or is pushed with overclocking, and it improves with undervolting, at the cost of a lower hashrate. Hydro-cooled and immersion-cooled models generally show better figures than their air-cooled equivalents. Always compare two models running the same algorithm in the same mode.
Our ASIC profitability calculator takes efficiency into account, and our HappyMining firmware, installed free of charge on machines bought from us, helps you find the most efficient setting.