Efficiency, not hashrate, decides what you pay per coin

Every spec sheet leads with terahash. It is the easiest number to compare and the one manufacturers put in the model name. But hashrate on its own tells you nothing about what a machine costs to operate. Two miners with identical hashrate can differ by a third in power draw, and that difference lands in your electricity bill every hour for years.

What J/TH actually measures

Efficiency is stated in joules per terahash: how much energy the machine spends to do one terahash of work. Lower is better. A machine at 15 J/TH consumes roughly a fifth less power for the same output than one at 19 J/TH. Over a fleet and over a year, that gap is usually far larger than the price difference between the two machines.

The arithmetic is simple enough to do on a napkin. Multiply efficiency by hashrate and you get wall power. Multiply wall power by your electricity rate and by hours of operation and you get running cost. Nothing about that calculation involves the coin price, which is why it is the one part of a mining plan you can actually pin down in advance.

Read the small print on the number

• Wall power or chip power. Some sheets quote the power draw of the boards only, excluding conversion losses in the PSU. Always compare wall figures, the number the meter sees.
• Rated ambient. Efficiency figures assume a temperature range. A machine run hot throttles, and a throttled machine has worse real efficiency than its sheet.
• Tolerance. Manufacturers publish a tolerance band, often several percent. Batch to batch variation is normal, so treat the figure as a centre point, not a guarantee.

When the less efficient machine still wins

Efficiency is not the only variable. If your power is very cheap, or intermittent, or curtailed, capital cost per terahash can matter more than joules per terahash. A cheaper, thirstier machine that pays for itself faster can be the better buy on a site where energy is close to free but capital is tight. On expensive grid power the logic inverts sharply: there, efficiency is nearly the whole decision.

That is also the reason we quote hardware only after a short conversation about your power situation. Recommending a flagship to someone with cheap curtailed energy, or a bargain machine to someone on industrial grid rates, would be selling the wrong box.