A Bitcoin miner's spec sheet is short, but every line changes what the machine earns and costs. Here is how to read one, and how to compare two.
By Michal Beno, CEO, OneMiners26 October 2026
Three lines on a spec sheet decide almost everything: hashrate (TH/s) sets what a Bitcoin miner earns, power (W) sets what it costs to run, and efficiency (J/TH), which is simply watts divided by TH/s, tells you how much power each unit of work needs. Cooling, noise and voltage decide where it can run. Price per TH and break-even power price decide which one to buy.
245 TH/s
Antminer S21 Pro hashrate
3,675 W
power draw
15.0 J/TH
efficiency
$0.111
break-even per kWh today
OneMiners catalogue, 6 October 2026. Break-even at hashprice $0.0398 per TH/s per day, 5 October 2026, power only.
KEY TAKEAWAYS
The spec sheet, line by line
Every Bitcoin miner listing carries the same handful of numbers. Here they are for one real, popular model, the Antminer S21 Pro 245 TH/s, with what each line means and what to check.
Antminer S21 Pro 245T: what each line means
Hashrate, power, efficiency, cooling and price: OneMiners catalogue, 6 October 2026. Noise and input voltage: ASICMinerValue and MiningNow model pages, checked 6 October 2026.
Hashrate (TH/s): what the Bitcoin miner earns
Hashrate is how many guesses per second a Bitcoin miner makes at Bitcoin's puzzle. One TH/s (terahash per second) is one trillion guesses. Revenue scales directly with it. At today's hashprice, the industry's measure of revenue per unit of hashrate, of about $0.0398 per TH/s per day, 245 TH/s earns about $9.75 a day before costs.
Two things to know. First, hashrate on a sheet is a nominal figure with a tolerance: Hashrate Index notes the S21 Pro family is quoted within roughly 3% on hashrate and 5% on power. Second, the machine's hashrate never changes, but its share of the network does. When network hashrate rises, currently about 970 EH/s, each TH/s earns a little less bitcoin.
Watts and J/TH: what the Bitcoin miner costs to run
Power (W) is how much electricity the machine draws at any moment. Multiply by 24 hours and divide by 1,000 to get kilowatt-hours (kWh) per day, the unit your electricity bill uses. The S21 Pro uses 88.2 kWh a day: at $0.048 per kWh that is $4.23; at $0.17 it is $14.99.
Efficiency (J/TH), joules per terahash, is the cleanest single number for comparing Bitcoin miners of different sizes. A joule per second is a watt, so J/TH is just watts divided by TH/s. You can and should check it yourself on every listing.
THE SPEC SHEET FORMULAS
J/TH = W / TH/s (3,675 / 245 = 15.0)
kWh per day = W x 24 / 1,000 (= 88.2)
Break-even $/kWh = 0.0398 / (24 x J/TH / 1,000) (= $0.111)
Price per TH = price / TH/s (2,299 / 245 = $9.38)
Check it yourself: watts / TH/s = J/TH
Antminer S21 200T
Antminer S23 Hyd 580TWatts and TH/s from the OneMiners catalogue, 6 October 2026; J/TH computed. Every row matches the efficiency printed on its listing.
Efficiency across current Bitcoin miners
Joules per terahash, lower is better
Manufacturer specs as listed on the OneMiners catalogue, 6 October 2026.
Cooling, noise and voltage: where it can run
These lines do not change what a Bitcoin miner earns, but they decide whether you can run it at all.
Cooling. Air-cooled units use high-speed fans and need a vented room. Hydro units connect to a water loop that carries heat to an outside cooler; they allow denser racks and higher hashrate per unit, but need plumbing. Immersion setups sink miners in a non-conductive liquid.
Noise (dB). The S21 Pro is listed at about 75 to 76 decibels, similar to a vacuum cleaner that never switches off. Hydro units are much quieter at the box, because there are no big fans.
Voltage and phase. The S21 Pro takes 220 to 277 V AC. At 240 V it pulls about 15.3 amps, more than a standard 120 V U.S. socket can supply. The Antminer S21+ Hyd 395T is listed for 380 to 415 V three-phase power, which is industrial wiring, not a home circuit.
Plug, dimensions and weight. Check these on the seller's own sheet for your exact batch. Third-party spec databases list different box sizes and weights for the same S21 Pro model, so they are not reliable for planning shipping or rack space.
This is where hosting earns its keep. A facility already has the high-voltage circuits, water loops and noise-proof halls. You buy the Bitcoin miner; the site supplies the environment, billed per kWh.
How to compare two Bitcoin miners: a worked example
Take two air-cooled Bitcoin miners from the OneMiners catalogue: the Antminer S21 Pro 245T at $2,299 and the newer, more efficient Antminer S23 318T at $6,899. Which is better depends on what you are optimising for.
Antminer S21 Pro vs Antminer S23: the numbers that matter
Specs and prices: OneMiners catalogue, 6 October 2026. Hashprice $0.0398 per TH/s per day, subsidy only, 5 October 2026. Power only; excludes pool fees. Payback assumes today's numbers hold; difficulty usually rises, so real payback tends to be longer.
Read it in two directions. The S21 Pro is the cheaper way to buy hashrate, at $9.38 per TH against $21.69, so at today's numbers it repays its price faster on cheap power. The S23 makes more per day and keeps covering its power up to $0.151 per kWh, versus $0.111 for the S21 Pro. That extra margin is what protects you if hashprice falls or the network grows.
Daily net at three power prices
USD per day after power, before pool fees
Revenue = TH/s x $0.0398; power = W x 24 / 1,000 x rate. OneMiners calculation, data as of 5 and 6 October 2026. The gap widens as power gets dearer.
The rule of thumb: on cheap power, price per TH matters most. On expensive power, J/TH matters most. Either way, a lower power price improves every line.
Price per TH across the catalogue
Unit price divided by TH/s, USD
Live prices, OneMiners catalogue, 6 October 2026. Cheaper hashrate usually comes with higher J/TH; compare both.
Spec sheet traps to avoid
Check J/TH against the maths
Divide watts by TH/s. If the printed J/TH is lower than your answer, the listing is flattering the machine.
Know the tolerance
Hashrate and power are nominal figures with a few percent of tolerance either way. Plan on the printed numbers, not better.
Watch the batch date
The same Bitcoin miner can be sold in stock or for later delivery at a very different price. A later batch costs less but earns nothing until it arrives.
Match the voltage to the site
High-voltage single-phase and three-phase units cannot run on a home socket. Check before you buy.
Read the warranty terms
Warranties cover defects, not normal wear. Check who repairs the unit and where it has to be shipped.
Same Bitcoin miner, different batch date, different price
Antminer S23 Hyd 3U 1160T
Antminer S23e Hyd 2U 865TVariant prices on the OneMiners catalogue, snapshot of 24 September 2026. Prices change; check the live listing. A later batch starts earning later, when network hashrate may be higher.
A later batch at half the price can be a good deal, but compare it properly: count the months with no revenue, and assume the network will be bigger when it switches on. An in-stock unit starts earning as soon as it is installed.
Antminer S21 Pro 245T$2,299Hashrate245 TH/sEfficiency15.00 J/THPower draw3,675 WBreak-even power$0.111/kWhNet/day at 4.80c$5.52View on OneMiners
Antminer S23 318T$6,899Hashrate318 TH/sEfficiency11.00 J/THPower draw3,498 WBreak-even power$0.151/kWhNet/day at 4.80c$8.63View on OneMiners
Antminer S21+ Hyd 395T$2,499Hashrate395 TH/sEfficiency15.00 J/THPower draw5,925 WBreak-even power$0.111/kWhNet/day at 4.80c$8.90View on OneMiners
The three Bitcoin miners used in this guide, live prices 6 October 2026. Card figures use hashprice including recent fees, so they can differ slightly from the subsidy-only examples.
A spec sheet is a promise about the machine. What it earns for you depends on one number that is not on the sheet: your power price. OneMiners hosts Bitcoin miners from $0.048 per kWh, and from $0.0364 on a 7-year prepaid contract, with a 7-year warranty on hosted miners that covers defects, not normal wear. Run any model through the mining calculator before you choose.
Frequently asked questions
What is a good J/TH for a Bitcoin miner in 2026?
The newest hydro units on the OneMiners catalogue reach about 9.5 J/TH, and new air units about 11 J/TH. Units around 15 to 18 J/TH still cover their power on cheap electricity at today's numbers.
Is a higher hashrate always better?
Not by itself. A bigger Bitcoin miner usually draws more power too. Compare J/TH and price per TH, not hashrate alone.
How do I calculate a miner's daily power use?
Multiply watts by 24 and divide by 1,000. An S21 Pro at 3,675 W uses 88.2 kWh a day.
Can I run an Antminer S21 Pro at home?
Only on a high-voltage circuit: it takes 220 to 277 V and pulls about 15 amps at 240 V. It is also about as loud as a vacuum cleaner, around the clock.
What is break-even power price?
The highest electricity price at which a Bitcoin miner's revenue still covers its power bill. Divide hashprice by 24 x J/TH / 1,000.
Why is the same model cheaper for a later delivery?
Later batches earn nothing until they arrive, and the network is usually larger by then, so sellers price them lower.
Compare Bitcoin miners by J/TH and price per TH, then run your own numbers.
Open the mining calculatorBrowse Bitcoin minersSOURCES AND DATA
- Specs and live prices (TH/s, W, J/TH, cooling, price): OneMiners catalogue, 6 October 2026
- Batch-date variant prices: OneMiners catalogue snapshot, 24 September 2026
- S21 Pro noise (75 to 76 dB) and input voltage (220 to 277 V AC): ASICMinerValue and MiningNow model pages, checked 6 October 2026
- S21+ Hyd 395T input voltage (380 to 415 V three-phase): MiningNow model page, checked 6 October 2026
- Hashrate and power tolerance: Hashrate Index, Hardware Overview: Antminer S21 Pro, 10 April 2026
- BTC price $85,739: CoinGecko, 5 October 2026; hashrate and hashprice basis: mempool.space, 5 October 2026
- Hosting rates: published OneMiners location pages
Michal Beno
CEO of OneMiners, the global Bitcoin mining hosting and hardware platform with 15 published hosting locations, 7-year fixed electricity contracts and a 7-year hardware warranty. He writes about the economics of industrial Bitcoin mining.
Informational only, not financial advice. Figures are a snapshot from public market data and news reports as of 5 October 2026 and can change quickly. Crypto prices can fall as well as rise. No return is offered or implied. Do your own research.
