Every ASIC miner ships with a spec sheet, and once you know how to read one you can compare two machines in about a minute. Most of the marketing is noise. Four numbers decide whether a rig makes sense for you.
Hashrate: raw output
Hashrate is how many hashes per second the machine can compute, quoted in terahashes (TH/s) for Bitcoin SHA-256 miners. Higher is better, but hashrate alone tells you nothing about cost. A machine twice as fast that also draws twice the power has not improved your economics at all. Treat hashrate as the numerator, never the whole story.
Efficiency: the number that matters most
Efficiency is quoted in joules per terahash (J/TH) and it is the figure that separates a profitable machine from a space heater. It tells you how much electricity the miner burns for each unit of work.
A miner at 20 J/TH does the same work as one at 40 J/TH for half the power bill.
Because electricity is usually the largest ongoing cost, efficiency, not headline hashrate, is what determines whether a machine survives the next difficulty increase. When you compare rigs, sort by J/TH first.
Power draw and your supply
Power consumption is listed in watts. Two things to check:
- Your circuit and power supply can actually deliver it, with headroom. A machine rated at 3,500 W should not sit on a circuit rated for exactly that.
- The quoted wattage is measured at the wall at a stated temperature. Real draw rises as the room warms, so budget above the sticker figure.
Multiply watts by your electricity rate and your run hours to get the daily energy cost. That number, set against the coin you expect to earn, is your real margin.
Operating conditions
The last block of the sheet covers temperature and humidity ranges, noise, and cooling type. These are easy to skim and expensive to ignore. An air-cooled unit rated to 35 C ambient will throttle or shut down in a hot, unventilated room, and a machine that is comfortable in a data centre can be unbearably loud in a garage.
Putting it together
Read a spec sheet in this order: efficiency, then power draw against your supply, then hashrate, then operating conditions. A machine wins on efficiency and fits your power and climate long before its headline terahash figure matters. If a listing hides the J/TH number, that usually tells you why.
