The Antminer S19K Pro was Bitmain's efficiency benchmark when it launched. The S21 replaced it. And yet the S19K Pro is still being bought, still being discussed, and still sitting in home mining setups across Australia. So is it still worth buying in 2026 — or is the price gap between the two units not enough to justify the older machine's higher running costs?
This comparison breaks down both units across every metric that matters for Australian home miners: hashrate, efficiency, power draw, noise, and the all-important question of whether the cheaper purchase price actually saves you money once electricity costs are factored in.
Specifications at a Glance
| Specification | Antminer S19K Pro | Antminer S21 |
|---|---|---|
| Hashrate | 120 TH/s | 151 TH/s |
| Power Draw | 2760W | 2643W |
| Efficiency | 23 J/TH | 17.5 J/TH |
| Algorithm | SHA-256 | SHA-256 |
| Chip Process | 5nm (BM1362) | 5nm (BM1370) |
| Noise Level | ~75 dB | ~75 dB |
| Dimensions | 400 × 195 × 290 mm | 400 × 195 × 290 mm |
| Network | Ethernet | Ethernet |
Both units run the same SHA-256 algorithm targeting Bitcoin, use the same physical chassis footprint, and operate at similar noise levels. The differences that matter are efficiency and hashrate — and those differences compound significantly over time.
The Efficiency Gap Is the Real Story
The S19K Pro draws 2760W to produce 120 TH/s — that's 23 joules per terahash. The S21 draws 2643W to produce 151 TH/s — that's 17.5 J/TH. The S21 uses slightly less power while producing 26% more hashrate.
That's not a small difference. It's the gap between two chip generations, and it shows up directly in your electricity bill every single day.
Let's model it at a common Australian residential electricity rate of $0.30/kWh:
| S19K Pro | S21 | |
|---|---|---|
| Daily power cost | $19.87 | $19.03 |
| Monthly power cost | ~$596 | ~$571 |
| Annual power cost | ~$7,253 | ~$6,951 |
| Hashrate delivered | 120 TH/s | 151 TH/s |
At $0.30/kWh, the S21 costs roughly $300 less per year to run while producing significantly more hashes. At higher electricity rates — and many Australian households are on $0.35–0.40/kWh — that annual saving widens further.
This is before accounting for the hashrate difference. The S21 produces 31 TH/s more than the S19K Pro. At current network difficulty and Bitcoin price conditions, that additional hashrate translates to meaningfully more expected revenue per day. The S19K Pro doesn't just cost more to run — it also earns less.
Purchase Price: How Big Is the Gap?
The S19K Pro's main argument is price. As an older generation unit, it sells for considerably less than the S21 — and the gap between them is the core question of this comparison.
If the S21 is, say, $400–600 more expensive than the S19K Pro at current market prices, and the S21 saves you $300/year in electricity while earning more in hashrate revenue, the S21 pays for that price difference within 12–18 months of continuous operation. After that crossover point, the S21 is the better financial outcome every subsequent month.
If the price gap is larger — $800 or more — the payback period extends, and the S19K Pro becomes more defensible, particularly if you're on a constrained budget or planning to run the miner for a shorter period. See current pricing for both the Antminer S19K Pro and Antminer S21 to run your own numbers.
Electricity Rate Sensitivity
Electricity rate is the single biggest variable in this decision for Australian miners. The higher your rate, the more the S21's efficiency advantage matters — and the harder it becomes to justify the S19K Pro.
| Electricity Rate | S19K Pro Annual Power Cost | S21 Annual Power Cost | Annual Saving (S21) |
|---|---|---|---|
| $0.25/kWh | ~$6,044 | ~$5,793 | ~$251 |
| $0.30/kWh | ~$7,253 | ~$6,951 | ~$302 |
| $0.35/kWh | ~$8,461 | ~$8,109 | ~$352 |
| $0.40/kWh | ~$9,670 | ~$9,267 | ~$403 |
If you're on a high residential tariff — common in NSW, VIC, and SA — the S21's efficiency advantage becomes increasingly difficult to overlook. If you're on a cheaper commercial or off-peak rate, or running solar, the gap narrows and the S19K Pro becomes more competitive on a pure cost basis.
Resale Value Considerations
Hardware resale value is another factor worth modelling. Older generation miners depreciate faster than newer ones, and the S19K Pro is already one generation behind. If you plan to sell or upgrade within 12–24 months, the S19K Pro will have depreciated more steeply than the S21 by that point — meaning the effective cost of ownership is higher than the purchase price alone suggests.
Our guide on mining hardware resale value in Australia covers which ASICs hold their price best and how to factor depreciation into your buying decision. The general principle: newer, more efficient hardware depreciates more slowly because it remains competitive for longer on the network.
Who Should Still Consider the S19K Pro?
The S19K Pro is not a bad miner — it's a capable, proven unit that mines Bitcoin reliably. There are scenarios where it remains a reasonable choice:
- Very low electricity rates: If you're on $0.20/kWh or below (solar feed-in offset, commercial rate, or a favourable off-peak tariff), the efficiency gap shrinks enough that the lower purchase price becomes the dominant factor
- Short intended run time: If you plan to mine for 6–12 months and sell the hardware, and the purchase price difference is substantial, the S19K Pro may deliver acceptable returns before resale value diverges significantly
- Budget constraints: If the S21 is genuinely out of budget and the choice is between an S19K Pro or nothing, the S19K Pro still produces meaningful hashrate — just less efficiently
- Scaling an existing S19 operation: If you already have S19-era hardware and supporting infrastructure, adding an S19K Pro has lower incremental setup friction than introducing a new generation
Who Should Choose the S21
For most Australian home miners buying new hardware today with a 2–3 year time horizon, the S21 is the stronger choice. The efficiency gap is real, the hashrate advantage is material, and the S21 will remain competitive on the network for longer before being pushed into marginal profitability by difficulty growth.
If you want to understand what the next step up from the S21 looks like, our review of the Antminer S21 Pro covers whether Bitmain's flagship 234 TH/s unit justifies its premium over the base S21.
When to Upgrade From an Existing S19K Pro
If you already own an S19K Pro and are wondering whether to upgrade, the calculus is similar but slightly different. You're not comparing purchase prices from zero — you're weighing the cost of a new S21 (minus the resale value of your S19K Pro) against the ongoing electricity saving and revenue uplift the S21 would deliver.
Our guide on when to upgrade your miner walks through a data-driven framework for making this call, including how to factor in difficulty projections, Bitcoin price assumptions, and your local electricity rate.
The Verdict
The Antminer S21 is the better miner. It uses less power, produces more hashrate, and will hold its value longer. For Australian miners on typical residential electricity rates, the S21's efficiency advantage translates to meaningful savings that, over 12–18 months, recoup any price premium over the S19K Pro.
The S19K Pro still makes sense in specific situations — primarily very low electricity costs or tight budgets — but as a default recommendation for someone buying new Bitcoin mining hardware today, the S21 is the unit we'd point to.
View the Antminer S21 and Antminer S19K Pro side by side, or browse the full Bitcoin miners collection to compare all available options.
