Whatsminer M61S review: 18.5 J/TH in an air-cooled box, and Nigeria is where it pays best

Name: Whatsminer M61S review: 18.5 J/TH in an air-cooled box, and Nigeria is where it pays best
Item: MicroBT Whatsminer M61S
Rating: 4.5
Author: Firsthand Bitcoin

MicroBT's M61S makes 220 TH/s from 4,070 W in an air-cooled box, at 18.5 J/TH and the lowest entry price per terahash it has had. It clears its power at 6¢ today with less room than newer machines, and Nigeria's cheaper power is where it earns most.

Firsthand card: "Whatsminer M61S", review, 18.5 J/TH, 220 TH/s air-cooled, with the machine itself on a dark background

MicroBT Whatsminer M61S (220 TH/s)

The bottom line

The M61S is MicroBT's air-cooled Whatsminer at 18.5 J/TH: 220 TH/s from 4,070 W in the bin we list, 18.5 J/TH. In Argentina, at 6¢, it makes a bitcoin for about $62,200 of electricity and returns roughly 25% in its first year at today's price. At Nigeria's 3.9¢ the same coin costs about $40,500 and the first year returns 39%.

Bought once its price settled, in July 2025, it has mined and kept 0.0428 BTC for $2,461 of power: $1,027 of cashflow against a $4,304 landed cost, 24% of the box so far. Between now and the 2028 halving it has another 0.042 BTC in it, worth about $5,276 with bitcoin back at its previous high: roughly 1.5× its hardware by the halving, still running afterwards.

What you are buying is a low entry price per terahash on an air-cooled box that takes ordinary supply. What you are not buying is the cheapest coin: the M61S+ makes one for about $57,200 and the M60S++ for about $50,500 in the same room, against this machine's $62,200.

Scores

Criterion	Score	Why
Cashflow	4.5/10	Makes a bitcoin for about $62,200 of electricity at 6¢ and returns roughly 25% in year one at today's price. It has covered 24% of its hardware so far and is on track for about 1.5× by the 2028 halving. The M61S+ returns about 29%.
Longevity	4.5/10	At 18.5 J/TH its line is $26.64 a petahash a day at 6¢ and $17.32 at 3.9¢. Today's hashprice halved sits between the two, so after the halving it is a Nigeria machine, which is the move every machine makes once.
Efficiency	3.5/10	Near the bottom of what we stock in air: the M61S+ runs 17 J/TH, the M60S++ 15.5 and the S21 XP 13.5.
Quality control	5/10	Scored as unknown rather than as good. We found no operator reports of the M61S in the field that we could cite.
Serviceability	6.5/10	An air-cooled unit with no water loop to service. Hosted with us in Argentina, a fault is a parts bill and a line item.

Weighted on what an owner gets back per dollar over the next four years. A low entry price and a margin today carry it; 18.5 J/TH puts it near the bottom of the air-cooled range, and a reliability record we could not find holds it back.

Buy it if

You want hashrate at a low price per terahash: $6.20 for the M61S, against $7.14 for the M61S+ and $9.45 for the M60S++.
Your power is at or below 6¢. At 6¢ it makes a coin for about $62,200; at 3.9¢, about $40,500.
You expect to cross to Nigeria once, when the figures say so. At 18.5 J/TH its line there is $17.32 a petahash a day, under today's hashprice halved.
You want a 220 TH/s machine on ordinary single-phase supply, with no coolant loop.

Walk away if

You are planning past 2028 at 6¢. Its line there is $26.64 a petahash a day, and today's hashprice halved sits well below that, so those years lean on bitcoin recovering.
You want the cheapest coin. The M61S+ returns about 29% in year one against this machine's 25%, and the S21 XP makes a coin for about $45,400.
Your power sits between 3.9¢ and 6¢ and is not going down. Between those two lines the machine works today and goes marginal after the halving.
You want a public failure record. We found no operator reports of the M61S that we could cite, and we score that as unknown.

What MicroBT shipped

The M61S is an air-cooled Whatsminer from MicroBT. Our store lists ten bins from 204 to 222 TH/s, nine of them at 18.5 J/TH, and one at 216 TH/s drawing 4,320 W for 20 J/TH. The 220 TH/s bin used here is rated at 4,070 W, in a chassis 430 mm by 155 mm by 226 mm weighing 13.5 kg.

Those figures are our store record: we could not open MicroBT's own product page, and retailer listings disagree on hashrate, so we state only what the record holds. It sits below the M61S+ at 17 J/TH, and well below the M60S++ at 15.5 J/TH and the M70S at 13.5 J/TH.

Chart: Coins kept since the first settled price we hold for it, the electricity that made them, and where it lands by the 2028 halving.

Priced like a settled machine

The first price we hold for the 220 TH/s unit gave a purchase of $2,772 in July 2025. It is $1,363 today, $6.20 a terahash, for the same 220 TH/s at the same 18.5 J/TH. The hashrate did not change; only the entry price did, and a proven machine at a settled price is what the entry looks like now.

Against its neighbours, price per terahash tells the story. The M61S+ is $7.14 a terahash at 17 J/TH. The M60S++ is $9.45 at 15.5 J/TH. The M61S asks the least per terahash of the three and the most electricity per terahash, and the guide to what a miner costs all-in shows what sits on top of the box.

Chart: What the 220 TH/s unit has cost since the first price we hold for it, in July 2025.

What a coin costs it

At 6¢ in Argentina it makes a bitcoin for about $62,200 of electricity today, against a bitcoin price of $82,230. At Nigeria's 3.9¢ the same machine makes one for about $40,500. The M61S+ makes one in Argentina for about $57,200, and the M60S++ for about $50,500.

In its first year the M61S returns about 25% at 6¢ and 39% in Nigeria. The M61S+ returns 29% in Argentina and 39% in Nigeria, and the M60S++ 31% and 35%. The gap to the Nigerian figure is the point: this machine is made for cheap power.

Over its run since July 2025, electricity has averaged about $57,600 a coin. That is a lifetime average over 449 days; the figure to plan on is today's.

Chart: One bought today at today's price and racked in Argentina: year one at today's difficulty, and what it returns by the April 2028 halving with bitcoin back at its previous high.

Where the halving puts it

A machine's line is the hashprice at which it stops covering its own power. At 18.5 J/TH a petahash uses 444 kWh a day: $26.64 at 6¢, and $17.32 at Nigeria's 3.9¢. On our hashprice chart, the year's low was $27.74 a petahash a day on 6 June, so the 6¢ line sits just under last June's trough, and the Nigerian line well under it.

The 2028 halving halves the coins a petahash earns. At today's price and difficulty that puts hashprice at about half of today's, between the two lines: below the 6¢ one and above the Nigerian one. That is today's conditions held flat, not a forecast: it is why every projection we publish assumes the old high returns, and the forward figures here do the same.

So the machine is an Argentina machine now and a Nigeria machine after, and the move is made once. In our model of its run it crossed to Nigeria on 27 July 2026. The guide to crossing once explains why, and the guide to efficiency and halvings shows where the line sits at every J/TH. Our own look-back at the M61S follows one through it.

Chart: Network hashprice per petahash per day. The M61S needs about $27 of it at 6¢ and about $17 at 3.9¢; half of today's level falls between them. Open the chart

What a fault costs you here

We looked for operator threads and repair write-ups on the M61S and found nothing specific to it that we could stand behind, so the reliability score is unknown rather than good or bad. A machine close to two years in the field with no public record is not a warning, and it is not a clean bill of health either.

What a fault costs is the part that matters. Hosted with us in Argentina, a repair is billed at the cost of the parts and nothing else: a failed hashboard is a line item, not a catastrophe. An air-cooled unit has no coolant to drain and no cold plate to reseal, so a bench can work on it directly.

We found no operator reports of this machine's boards we could cite. We score that as unknown, not as good.

Chart: Scored on what costs an owner money over a four-year life. Reliability is scored as unknown.

Our two cents

The M61S is a sound machine at a settled price, and a plain one. At 6¢ it clears its power today, it needs Nigeria's cheaper power after the halving, and it makes the most of that power. A buyer who wants the lowest price per terahash in an air-cooled box has a reason to pick it.

Most buyers chasing the cheapest coin should look one step up: the M61S+ makes it for about $57,200 in Argentina, and the figure below ranks everything that beats this machine on cost per coin and then year-one return, in stock today. A coin that costs less to make is a coin you keep more of.

MicroBT Whatsminer M74S+ (332 TH/s) — 12 J/TH, In stock, $40,373 of electricity per bitcoin, 30% year one
MicroBT Whatsminer M73S (560 TH/s) — 13 J/TH, In stock, $43,737 of electricity per bitcoin, 35% year one
MicroBT Whatsminer M7DS (672 TH/s) — 13.5 J/TH, In stock, $45,420 of electricity per bitcoin, 36% year one

What beats it on cost per coin and on first-year return, in stock today.

Which machines this covers

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.