An ASIC miner profitability comparison should start with operating margin, not with the largest hashrate number. For SHA-256 miners, revenue is linked to hashrate, but the result that matters is what remains after electricity, pool fees, hosting, maintenance, downtime, and the machine’s purchase cost. A miner with a lower headline hashrate can be the stronger choice if it consumes less energy per terahash or fits the available site more reliably.

This review compares four air-cooled SHA-256 machines: the Antminer S21, WhatsMiner M60S+, Avalon A15 Pro, and Bitdeer SealMiner A2. The specifications provide a useful starting point, but they are not a fixed profit forecast. Bitcoin price, network difficulty, transaction fees, machine availability, and local energy pricing can all change the conclusion.

How to compare ASIC miner profitability

A practical comparison has two layers. The first is hardware efficiency: how much electricity is required to produce one terahash of work. This is normally expressed as joules per terahash (J/TH). Lower J/TH generally means lower electricity cost for the same amount of hashing.

The second layer is the operating environment. The same unit can have very different economics at a low-cost industrial site and at a higher-cost hosted or home location. A useful model should include:

• Hashrate in TH/s, for expected share of network rewards.
• Power draw in watts, for energy cost.
• Energy efficiency in J/TH, for a fast comparison of power intensity.
• Electricity or hosting price per kWh.
• Pool fee and expected uptime.
• Delivered machine price, shipping, import costs, and any site upgrades.
• Cooling, noise, electrical, repair, and warranty constraints.

Hashrate should be compared only among machines mining the same algorithm. All four units reviewed here are SHA-256 models, so their efficiency and power figures can be evaluated on a comparable basis.

The four-miner specification comparison

Antminer S21

BITMAIN specifies the Antminer S21 at 200 TH/s with 3,500 W power consumption at the wall and a 17.5 J/TH efficiency rating. That makes it a straightforward baseline for a modern air-cooled Bitcoin mining deployment. Its daily electricity demand is 84 kWh before considering facility overhead such as ventilation or auxiliary cooling.

The S21’s appeal depends on purchase price, condition, support access, and the site’s ability to provide the required 220–277 V input. Its efficiency is close to the other models in this comparison, but not the lowest on the stated specifications.

WhatsMiner M60S+

The reviewed listings for a 208 TH/s WhatsMiner M60S+ state 3,432 W of power consumption and 16.5 J/TH efficiency. At that rating, it offers more hashrate than the S21 while drawing slightly less power, giving it a better energy-efficiency position on paper.

However, miners should confirm the exact M60S+ configuration in the purchase documentation. Product listings and hashrate bins can differ, and the power rating must match the specific unit being quoted. The facility should also verify voltage, circuit capacity, connector requirements, and thermal design before deployment.

Avalon A15 Pro

The Avalon A15 Pro-221T is listed at 221 TH/s, 3,662 W, and 16.8 J/TH. It sits between the stated efficiency figures of the S21 and the two 16.5 J/TH machines. Its higher hashrate can be useful where per-unit deployment capacity matters, but its larger power draw produces a higher daily energy bill at the same tariff.

This does not automatically make it less attractive. If its delivered price, availability, warranty coverage, or repair path is more favorable for a specific operator, its total-cost result may still be competitive. Efficiency is important, but it is not the whole procurement case.

Bitdeer SealMiner A2

Bitdeer lists the SealMiner A2 at 226 TH/s, 3,729 W, and 16.5 J/TH. On the published numbers, it matches the M60S+ efficiency rating while providing the highest hashrate in this four-unit set. It also has the largest power draw, so each unit requires more electrical and cooling capacity than the other three models.

For a site constrained by rack positions rather than power, greater per-unit hashrate may be useful. For a site constrained by power availability, the added load and heat need to be weighed against the hashrate gained. Purchase price and delivery terms are particularly important here because a strong efficiency rating does not by itself establish a faster payback.

A like-for-like revenue and electricity-cost example

To compare the same operating conditions fairly, assume continuous operation, electricity priced at $0.06 per kWh, and the same current network, Bitcoin price, transaction-fee, pool-fee, and uptime assumptions for every machine. Gross revenue should be calculated from each miner’s hashrate using the same current revenue-per-TH/s input.

Daily gross revenue = hashrate in TH/s × current gross revenue per TH/s per day.

Using the July 13, 2026 gross-revenue input, the estimated daily gross revenue is:

• Antminer S21: 200 × $0.03128 = $6.256 per day.
• WhatsMiner M60S+: 208 × $0.03128 = $6.50624 per day.
• Avalon A15 Pro: 221 × $0.03128 = $6.91288 per day.
• Bitdeer SealMiner A2: 226 × $0.03128 = $7.06928 per day.

Daily electricity cost = power in kW × 24 × electricity price per kWh

Using the published or listed power ratings, the estimated daily machine-only electricity costs are:

• Antminer S21: 3.500 kW × 24 × $0.06 = $5.04 per day.
• WhatsMiner M60S+: 3.432 kW × 24 × $0.06 = about $4.94 per day.
• Avalon A15 Pro: 3.662 kW × 24 × $0.06 = about $5.27 per day.
• Bitdeer SealMiner A2: 3.729 kW × 24 × $0.06 = about $5.37 per day.

Estimated daily operating margin = daily gross revenue − daily electricity cost − pool fees − other operating costs

This provides a fairer comparison than electricity cost alone because the higher-hashrate machines also produce a larger expected share of mining revenue under the same conditions. The final margin still depends on live Bitcoin price, network difficulty, transaction fees, pool fees, downtime, and cooling overhead, so the revenue input should be refreshed when comparing purchase options.

At a different electricity rate, the ranking by energy cost stays the same, but the size of the cost gap changes. A low-cost site may have more flexibility to prioritize machine price or availability. A higher-cost site will usually place greater weight on energy efficiency and real uptime.

How to calculate a realistic profitability case

Use a miner profitability calculator as a scenario tool rather than a prediction engine. Begin with the exact model and hashrate bin, then enter the local electricity rate, applicable pool fee, and any daily operating charges. The output should show gross revenue, electricity cost, other costs, and estimated net operating result.

For each machine, test at least three cases:

1. A current-conditions case using the latest available network and market inputs.
2. A conservative case with lower revenue or higher difficulty and realistic downtime.
3. A stress case that includes a less favorable Bitcoin price, higher difficulty, or higher energy cost.

Then calculate payback using total deployed cost, not the miner’s sticker price alone. Total deployed cost can include shipping, customs, rack or container work, electrical distribution, transformers, ventilation, commissioning, spares, and hosting deposits. A nominally cheaper unit may not be cheaper after the site work required to run it.

Pool selection also belongs in the model. Payout method, fee structure, settlement approach, and the operator’s cash-flow needs affect how revenue is received. A pool calculator can provide a current snapshot, but its assumptions should be refreshed regularly because mining economics are dynamic.

Choosing between the four miners

On stated energy efficiency, the WhatsMiner M60S+ and Bitdeer SealMiner A2 are positioned at 16.5 J/TH, followed by the Avalon A15 Pro at 16.8 J/TH and the Antminer S21 at 17.5 J/TH. That difference is meaningful, especially for operators with expensive energy or large fleets, but it should not be converted into an unsupported universal ranking.

The better choice depends on the decision constraint:

• If electricity cost is the limiting factor, prioritize verified J/TH, measured power draw, and uptime.
• If rack space is limited, compare hashrate per unit alongside the site’s available power and cooling capacity.
• If capital is limited, compare delivered cost per TH and total deployed cost, not only daily operating margin.
• If maintenance access is limited, examine warranty terms, local repair capability, spare-part availability, and the operator’s experience with the model.
• If the site has electrical limits, verify the voltage, circuit, cable, and breaker requirements before ordering.

The S21 can serve as a familiar reference point. The M60S+ and SealMiner A2 may offer a stated efficiency advantage, while the A15 Pro offers a different balance of hashrate and power. The most defensible conclusion comes from applying the same live assumptions to each unit.

A practical pre-purchase checklist

Before committing to hardware, confirm the following in writing:

• Exact model, hashrate bin, power rating, and efficiency tolerance.
• Delivered price, shipping terms, taxes, and estimated delivery date.
• Warranty duration, exclusions, return process, and repair location.
• Site electricity rate, voltage, circuit capacity, and demand charges.
• Cooling design, ambient temperature range, noise limits, and heat-removal capacity.
• Pool fee, expected uptime, monitoring plan, and downtime assumptions.
• Current profitability output under base, conservative, and stress scenarios.

A disciplined ASIC miner profitability comparison is less about selecting a headline winner and more about identifying the machine that remains workable when the assumptions become less favorable.