How to Read an ASIC Spec Sheet
A BITMAIN specification page, or any other manufacturer's, describes reference conditions. It is neither a performance warranty nor a profitability model. The footnotes under the table usually matter more than the large TH/s figure at the top, and they are what explains the gap between the sheet and what your machine actually delivers in a hall.
Product glance against detailed characteristics
Sheets split into two parts:
- Product glance: algorithm, typical hashrate, wall power, wall efficiency, and sometimes a version code, for example S21 XP version 10, or S21 version L1-10 in the user guide.
- Detailed characteristics: voltage, current, dimensions, weight, noise, humidity, altitude, and fluid in the case of hydro models.
Reseller listings almost always copy the glance line alone, dropping the reference temperature and the tolerances. That is the first thing to go and find on the original sheet.
Typical hashrate is not a floor
On the S21 and S21 XP pages, hashrate is explicitly labelled typical. The printed note states that actual hashrate fluctuates by ±3 %, and wall power and efficiency by ±5 %.
Two consequences for a buyer. A pool dashboard slightly below the typical TH/s is not by itself proof of a defective machine. And a brief spike above typical is no proof that you were shipped a better bin either.
Some families publish several typical hashrate columns under a single model name. The S21 user guide lists 200, 195, 188, 175, and 151 TH/s for model S21, while the Support article shows only the 200 TH/s headline bin. Always match the model string with the column, never a reseller nickname such as "S21 151T".
Reference temperature and wall measurement
Power and J/TH are given on wall, at a stated inlet temperature: 25 °C air on the S21 and S21 XP air sheets, 35 °C water on several Hyd sheets. "On wall" means facility-side AC after the PSU, not an estimate taken from a 12 V rail.
If your hall or your inlet water runs hotter than that reference, the glance watts no longer apply. The Support articles for the S21 XP include curves of hashrate and J/T against ambient: those curves describe your real situation, the headline does not.
An altitude note applies to the S21 and S21 XP: between 900 m and 2000 m, maximum operating temperature drops by 1 °C per 300 m. A mountain site therefore loses thermal headroom before a single machine is switched on.
J/TH, J/T, J/Ksol
BITMAIN mixes unit labels for the same figure: the shop writes J/TH, while Support tables use J/Ksol or J/T. For SHA-256 miners as published today, all three labels mean joules per terahash. Do not convert anything and do not correct the number.
In the S21 multi-bin table, the efficiency shown is 17.5 J/T for every listed hashrate, with wall watts scaling with the bin. A lower-hashrate S21 therefore sits in the same efficiency class, unless a sheet says otherwise.
Voltage, current, and adapted power
The air S21 and S21 XP sheets specify 220 to 277 V AC. A 110 or 120 V circuit is outside that window, and BITMAIN states that unsuitable voltage may damage the server.
Current, 20 A single-phase on these air units, is a supply-planning figure, often at a stated maximum condition. Take care not to confuse two lines: the adapted AC output power requirement, 4,000 W on the S21 and S21 XP tables, describes the PSU and PDU class, not the typical 3,500 or 3,645 W load. Size breakers and cords from the current and adapted-power notes, then measure real wall watts once the machine is installed.
The hydro SKUs, S21 Hyd and S21 XP Hyd, use a 380 to 415 V three-phase class. Copying an air sheet's voltage onto a hydro machine is the most expensive misread on this list.
Size, weight, noise, airflow
- Dimensions without package and with package differ by tens of millimetres. Rack planning uses the unboxed size, logistics uses gross weight.
- Weights published by Support include the PSU, which is not true of every manufacturer.
- Advertised noise is generally a maximum at maximum fan RPM, 76 dBA on these air sheets, sometimes measured at 30 °C. It is not an operating average.
- Maximum airflow in CFM, where present, comes from a fan curve. The S21 guide notes that dust and poor ventilation reduce it.
When the shop and Support disagree on a dimension, as seen on S21 XP length, do not average the two. Measure the unit you receive and keep that value.
Cooling class is part of the model name
Air, hydro, and immersion are different products, not options on one product. The inlet medium, the voltage, the footprint, and the J/TH reference temperature all change between classes. An "S21 XP" figure never applies to an "S21 XP Hyd", and the confusion between them is common in resale listings.
What the sheet does not cover
A spec sheet says nothing about bitcoin price, network difficulty, pool fees, your uptime, or your electricity rate. It does not certify the condition of a used machine, and it does not replace a wattmeter. Installed firmware, pool URL, and hosting contract all sit outside the table.
Put another way, the sheet gives you the denominator of your calculations, never the numerator.
A six-point reading checklist
- Record the official model and version, not just the TH/s nickname the seller uses.
- Check whether a value is typical or minimum, and note the tolerances.
- Note the reference inlet temperature and medium, air or water.
- Record voltage and phase, then current and adapted power to size the PDU.
- Confirm the cooling class and any associated fluid constraints.
- Keep the date and URL of the sheet consulted, preferring Support and the guide PDF over a reseller table.
Those six points take ten minutes and head off nearly every unpleasant surprise on delivery.
Sources
- BITMAIN Support, S21 XP Specifications: https://support.bitmain.com/hc/en-us/articles/35383015643673-S21-XP-Specifications
- BITMAIN Support, S21 Specification: https://support.bitmain.com/hc/en-us/articles/23794895251609-S21-Specification
- BITMAIN S21 User Guide V1.2.5: https://file12.bitmain.com/shop-product-s3/firmware/c17a60d7-51c8-41a3-8365-b7e5d1506caa/2025/04/10/14/S21%20User%20Guide-V1.2.5.pdf
- BITMAIN Support, S21 XP Hyd Specification: https://support.bitmain.com/hc/en-us/articles/34523540504857-S21-XP-Hyd-Specification
- BITMAIN Support, ANTMINER Specifications index: https://support.bitmain.com/hc/en-us/sections/360002496253
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