Manufacturer spec sheets are marketing documents. They lead with the number that looks best and bury the number that decides whether you make money. Here is how to read one properly.
Number 1: J/TH, not TH/s
Hashrate is the headline. Efficiency is the business.
J/TH (joules per terahash) tells you how much electricity the machine burns to produce one unit of work. It is the only spec that survives contact with your power bill.
A machine at 30 J/TH and a machine at 17 J/TH can advertise similar hashrates. At scale the second one prints money and the first one is a space heater. Work it out:
Daily power cost = (watts / 1000) x 24 x your $/kWhA 3,000W unit at $0.10/kWh costs $7.20 a day to run. At $0.16/kWh it costs $11.52. That $4.32 per day per machine is the entire margin on most units at most difficulty levels. Efficiency is not a tiebreaker, it is the whole decision.
Rule of thumb for 2026: under 20 J/TH is competitive. Over 30 J/TH only makes sense if your power is nearly free or you are buying for heat rather than hash.
Number 2: Real wall draw, not rated draw
Spec sheets quote power at a specific ambient temperature, usually 25C, on a specific firmware, at a specific voltage. Your garage in August is not 25C.
Expect real draw 5 to 10 percent above the sheet. Then size your circuit above *that*. A machine rated 3,250W will pull closer to 3,500W on a hot day, and you do not want to discover your breaker’s opinion about that at 2am.
Also check the PSU input voltage range. Plenty of high-end units will not run at 120V at all, or will run at heavily reduced output. If your building is 120V only, that eliminates a large chunk of the market before you start.
Number 3: The warranty term and who honours it
This is the spec that separates a real vendor from a drop-shipper. Look for:
- Length in months, and whether it starts at shipment or at delivery
- Whether it covers hash boards specifically, or only the control board and PSU
- Who performs the repair, and on which continent
- Whether opening the unit to clean it voids anything
A 180-day warranty that requires shipping a 15kg machine overseas at your cost is functionally a 0-day warranty. Ask the question before you buy, not after a board dies.
The specs that matter less than you think
- Advertised noise level. Always measured in ideal conditions. Assume 5 to 10 dB worse in a real room.
- Dimensions. Relevant only if you are racking. Otherwise noise and heat constrain you long before size does.
- “Profitability” figures on the product page. These assume a coin price and a difficulty that may be months stale. Always recalculate yourself.
Putting it together
The order of operations that keeps people out of trouble:
- Establish your real, all-in cost per kWh, including any demand charges.
- Filter to machines under your J/TH threshold at that power price.
- Filter again to what your electrical service can actually support.
- *Then* look at price and hashrate.
Most people run this list backwards, starting with hashrate and price, and end up with a machine they cannot power or afford to run.
If you want a catalog where the efficiency figures are listed per unit rather than buried, mininggearco.com groups its stock by algorithm and by coin, so you can compare like against like. Their shop-by-category hub is the fastest way in, and if you want to test a specific machine against your own power price before committing, run it through their profitability calculator first.
One last thing
Buy for the difficulty you expect in twelve months, not the difficulty today. Network difficulty has trended up for essentially the entire history of Bitcoin. A machine that is marginal at today’s difficulty is unprofitable at next year’s. Efficiency is what buys you time.