Guide · Oct 1, 2026 · 6 min read
How to read a bitcoin miner's spec sheet: the five numbers that matter
A spec sheet has two dozen lines and five of them decide whether a machine pays. Here they are in the order to read them, with two real machines worked through, so you can do the sum yourself before you buy anything.
A spec sheet is a short story with five facts
Every miner comes with a page of specifications, and the first time you read one it looks like a wall of numbers. Most of them are about fitting the machine into a room: size, weight, plugs. Only a handful tell you what it will earn.
Read them in this order: how much it computes, how much power it draws, how much power each unit of computing costs, what kind of room it needs, and how it will behave once it is switched on. The first three give you the money. The last two tell you whether you can actually run it.
We will use two real machines throughout, one old and one current, so every number has something to be compared with.
Hashrate: how much work it does
Hashrate is how many guesses per second the machine makes at the puzzle that earns bitcoin. It is written in terahashes per second, TH/s. One terahash is a trillion guesses. A modern machine does hundreds of them.
Hashrate is the machine's share of the network. The whole network is measured in exahashes per second (EH/s), a million times bigger, and bitcoin is paid out in proportion to your share of it. A machine that does twice the TH/s earns twice the coins, if everything else is equal.
Our two examples: the Antminer S19 Pro, from 2020, is rated at 110 TH/s. The Antminer S21 XP, from 2024, in its air-cooled version, is rated at 270 TH/s.
Power: what it draws from the wall
Power is how much electricity the machine uses while it runs, written in watts, W. A kilowatt is a thousand watts, and your electricity bill is charged per kilowatt-hour: one kilowatt for one hour.
The S19 Pro draws 3,250 W. The S21 XP draws 3,645 W. So the newer machine uses about 12% more power, and does about two and a half times the work. That already tells you something, and it is why the next number is the most important one on the sheet.
Power is also a typical figure, not an exact one. Bitdeer, for example, lists its A3 Pro Hydro at 8,250 W typical, with a range of 7,875 to 8,625 W. Plan for the top of the range.
Efficiency: the number that decides everything
Efficiency is written in joules per terahash, J/TH, and it is simply watts divided by TH/s. The S19 Pro is 3,250 ÷ 110 = 29.55 J/TH. The S21 XP is 3,645 ÷ 270 = 13.5 J/TH. The newer machine does the same work for less than half the electricity. Efficiency is a rating with a tolerance: Bitdeer lists 12.5 J/TH for its A3 Pro Hydro with a margin of plus or minus 5%, so the real figure can sit a little either side.
Here is what that means in money. Every J/TH is 0.024 kWh of electricity per terahash per day. At 6¢ a kilowatt-hour, the S19 Pro's electricity for one terahash is about 4.3¢ a day, and the S21 XP's is about 1.9¢.
Against that, what does a terahash earn? The network's average is called hashprice: how many dollars one petahash, a thousand terahashes, earns in a day. On 30 September it was $39.77 on our hashprice chart. That is 4.0¢ per terahash per day. The hashprice guide has the full story.
So at 6¢ the S21 XP earns about 4.0¢ and spends about 1.9¢ per terahash, a wide margin. The S19 Pro earns the same 4.0¢ and spends about 4.3¢: at 6¢ it would lose a little every day. At 3.9¢ it would spend about 2.8¢ and make a profit again. That is the whole logic of why efficiency decides how long a machine survives, and why older machines belong where power is cheapest.
Efficiency is power divided by hashrate. Lower is better, and it decides how long a machine keeps paying.
Cooling and voltage: what room it needs
The next lines tell you whether the machine will run where you want to put it. Cooling says how heat leaves the machine: air (fans), hydro (water through cold plates on the chips) or immersion (the whole machine submerged in a non-conductive fluid). Air-cooled machines are loud and need airflow. Hydro and immersion machines are quiet but need a loop or a tank, and a site built for them.
Voltage is the supply the power supply accepts. The S19 Pro takes 200 to 240 V and the S21 XP 220 to 277 V, which many industrial supplies provide. Many water-cooled and immersion machines, such as the S21 Immersion, run at 380 to 415 V, which means a three-phase supply. A machine on the wrong voltage will not start.
This is where buyers get caught. A hydro machine can be cheap partly because fewer people have a room that can run one. Hosting solves it, because the room is already built: that is the point of the all-in price, which covers the setup as well as the box.
Noise, weight and temperature: how it behaves
The remaining lines are about living with the machine. Noise is listed in decibels: the S19 Pro is rated at 75 dB and the S21 XP at 76 dB, about as loud as a vacuum cleaner right beside you, which is why these machines do not belong in a house. The water-cooled kind are far quieter, and an immersion machine like the S21 Immersion is rated at 50 dB.
Weight and dimensions matter for racking. The S21 XP weighs 18.7 kg and the S19 Pro 14.2 kg, both about 400 × 195 × 290 mm. A rack-mounted water-cooled unit can weigh over 40 kg, which needs rated shelving and two people.
Operating temperature is the range the room can be in. The S19 Pro is rated for 0 to 40 °C. In a hot country that range, not the hashrate, is what decides which months the machine runs flat out.
Five questions to ask before you buy
Put it together and a spec sheet reduces to five questions. How many terahashes is it? How many watts does it draw, and at what range? Divide the two: what is its efficiency in J/TH, and how does that compare with today's hashprice at the power price you will pay? What room does it need, and is that room already built? And what will it cost in total to have it running, not only to buy the box?
Here is the sum for the S21 XP at 6¢. It uses 3.645 kW for 24 hours, 87.5 kWh a day, which costs $5.25. At a hashprice of $39.77, its 0.27 petahash earns $10.74. The difference, about $5.49 a day before anything else, is what the five numbers add up to.
If you can answer those five, you know more about the machine than most of the pages that sell it. The questions you cannot answer from the sheet, such as how it ages and how often boards fail, are what a review is for.
One last point. Two machines with the same hashrate are not equal, and a better efficiency number is not a reason to pay any price. Check the entry price against what the machine earns, and the repair terms against where it will live: a failed hashboard is a line item, not the end of the plan, as long as you know where it gets repaired.
Disclosure
Firsthand Bitcoin sells and hosts mining hardware, including this machine. No manufacturer, distributor or affiliate programme paid for or reviewed this page and we take no commission on the links above. Historical figures are computed from daily bitcoin price and network hashprice, each day valued at its own prices. Nothing here is investment advice.