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Guide · Oct 12, 2026 · 5 min read

Why your miner's hashrate reads lower than its spec sheet, and when to worry

The box says 270 TH/s and the pool says 240. Almost always nothing is broken: the two numbers are counted in different ways, over different windows. Here is how to tell a normal wobble from a real fault, and what a real one costs.

Firsthand card: "Why your miner's hashrate reads lower than its spec sheet, and when to worry", with 270 TH/s as the rated hashrate of an Antminer S21 XP beside a jagged line of the network's daily hashrate over the last year

TL;DR

The number on the box and the number on the pool rarely match

Soon after a machine starts, most new owners notice the same thing. The spec sheet says the machine does 270 terahashes a second. The pool page says 240, then 285, then 262. It is natural to think something is wrong.

Usually nothing is. A rating and a reading are two different things, produced by two different counters. This guide explains each counter, then gives you a short routine for deciding whether a gap is noise or a fault.

If the units themselves are new to you, the spec sheet guide explains hashrate and efficiency first.

Your miner and your pool count in different ways

The machine's own screen works out its hashrate from what its chips are doing, mainly their clock speed. Foundry USA Pool, one of the large pools, puts it plainly: management software mostly gets its figure from CGMiner, which "calculates hashrate based on the clockspeed of the mining machine".

The pool cannot see your chips. It can only see the work your machine sends back. Foundry says it "estimates your hashrate based on the total accepted share difficulty we receive". A share is a small proof of work that the machine submits to the pool; the pool counts the accepted ones and turns the total into a speed.

So the miner reports what it believes it is doing, and the pool reports what it has received and accepted. Foundry adds that the share method "will have more variance and does not include stale and rejected hashrate". Both numbers are honest, and both are approximations.

One counter reads the machine's speed. The other counts the work that actually arrived.

A pool's live figure is an average of a short window

Shares arrive in a random pattern, so a count over a few minutes jumps around even when the machine is perfectly steady. Think of counting cars passing a window for ten minutes: some ten-minute stretches have more, some fewer, and the road has not changed.

The window matters. ViaBTC, another pool, says in an explainer dated 31 August 2026 that its real-time pool figure is "calculated from the average hashrate of the previous 10 minutes", while the miner's own screen may refresh about every five seconds. The two are looking at different slices of time. ViaBTC notes its windows are its own, so check the pool you use.

The fix is to widen the window. A day's average is steadier than ten minutes, and a week's is steadier still. If you remember one rule from this guide, make it that one: judge a machine on a week, not on a reading.

Four ordinary reasons a reading dips

Just started or restarted. ViaBTC says miners "may take roughly 10–15 minutes to stabilize, with some models taking around 30 minutes". A reading taken during that time is not the machine's real speed.

A young day. A pool's 24-hour figure counts the whole day. A machine switched on at noon has half a day of nothing in it, so the pool's daily number looks low while the miner's own screen looks fine.

Rejected and stale shares. Work that arrives late or is refused does not count for the pool. ViaBTC lists a slow or unstable connection among the causes. The machine still thinks it did the work.

A change of settings. Firmware updates, power events and a switch to a different pool address can leave a short gap. ViaBTC lists these among the recent operating changes that cause temporary dips.

None of these is a fault in the machine, and all of them clear on their own within the hour or the day.

When a gap is real

A real problem looks different. It is steady, it lasts, and it does not come back by itself. Three patterns are worth acting on.

A lower step that stays. The week's average sits well under the rating, day after day, and the line looks like a staircase rather than a wobble. On a machine with several boards, a lost board takes a fixed slice of the speed. The repair guide explains what that costs and who fixes it.

Rejected shares on one machine. ViaBTC says invalid shares on one unit can point to heat, unstable power, firmware problems, aggressive tuning or a hashboard fault. If the pool shows a worker with a high reject count beside its neighbours, that machine needs a look.

Many machines dropping at once. ViaBTC notes that when many miners fall together, the cause is more likely in shared equipment such as the router, switch or internet line than in many machines failing on the same day. That is a site problem, and it is the host's to fix.

Time offline is a separate matter, and the uptime guide covers it.

A four-step check you can do in ten minutes

Step one: wait. If the machine started or restarted in the last hour, look again later.

Step two: widen the window. Open the pool's chart and look at the last seven days, not the last ten minutes. Note the average.

Step three: compare it with the rating from the spec sheet. A week that sits a few percent under the rating is a normal machine. A week that sits a fifth or more under, with no outage to explain it, is worth a message.

Step four: write to your host with the dates, the average and what you expected. If you host with us, the machine's page in the owner portal shows the same picture. A message with numbers gets a faster answer than one that says the hashrate looks low.

Here is how it looks with made-up numbers. Three ten-minute readings on an afternoon say 240, 285 and 262 TH/s on a machine rated at 270. Each one looks different from the rating, but together they average 262, and a week of them might average 268. That machine is healthy. Compare it with a machine whose week averages 215 and whose chart shows the drop on one particular day: that is a staircase, and it is the one to chase.

Chart: What one petahash earned in bitcoin each day over the past year. Every figure here is a daily value: the chart moves over weeks, which is the timescale to judge a machine on. Open the chart

What a real shortfall costs, in bitcoin

The sum is short. On 12 October 2026 our hashprice chart showed a petahash earning about 0.000476 bitcoin a day. An Antminer S21 XP rated at 270 TH/s, which is 0.27 petahash, would earn about 0.000129 bitcoin a day at that rate, worth about $10.75 at the day's price of $83,677 (the store page lists the machine).

If a fault took a tenth of that speed away, the loss would be about 0.0000129 bitcoin a day, roughly $1.08. It is a real cost and a small one, which is why the answer to a lower reading is a calm check and a message, not an alarm.

A pool reading that dips for ten minutes costs nothing at all, because the machine kept working and the shares are still counted over the day. What counts is the long average, and what you do when it stays low. Output is not guaranteed, and it moves with the network, but the bitcoin a healthy machine mines is yours to keep.

Sources and further reading

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.