MB/s vs IOPS in AS SSD: What Each View Shows
Buried in AS SSD Benchmark’s View menu is a switch that rewrites every speed in the results grid: MB/s or IOPS. Same test, same run, two different languages — and endless forum confusion when one person’s screenshot is in one unit and another’s is in the other. This page explains what each unit actually measures, how to convert between them (with a worked example built from a published review result), and which view to use for which job. If you have not run the test yet, it is on our download page.
The two units, defined plainly
MB/s (megabytes per second) is throughput: how much data moved per second. It answers “how much?” and it scales with block size — streaming a 1 GB file produces a huge MB/s figure because each request carries a large payload. IOPS (input/output operations per second) is a count of requests completed per second, regardless of how much data each carried. It answers “how many?” and it exposes the per-request cost that throughput hides: a drive completing 100,000 tiny requests per second is working very differently from one completing a few hundred enormous ones, even if both show the same MB/s. Neither unit is more correct; they describe different properties of the same behaviour, which is why the tool offers both.
How the conversion works
The two units are linked by block size, through one identity: throughput = IOPS × block size. For the 4K rows, the block size is 4 KB, so each IOPS is worth 4 KB/s of throughput. That gives the practical conversions for any 4K figure:
IOPS = (MB/s × 1,024) ÷ 4 and MB/s = (IOPS × 4) ÷ 1,024
A worked example from a published result: in its Phison E12 reference-drive review, Legit Reviews reported the 4K-64Thrd row in IOPS — 441,299 IOPS read and 427,221 IOPS write. Convert the read figure: 441,299 × 4 KB = 1,765,196 KB/s, which is approximately 1,724 MB/s in the MB/s view. Run the same review’s single-thread 4K read of 57 MB/s the other way — 57 × 1,024 ÷ 4 ≈ 14,592 IOPS — and you can see why reviewers quote IOPS for random tests: “fourteen and a half thousand operations per second” communicates the request rate that “57 MB/s” conceals. Note that the sequential row does not convert this way in any useful sense, because the Seq test streams a 1 GB file rather than issuing 4 KB requests; IOPS is a meaningful lens for the 4K and 4K-64Thrd rows, not for Seq.
When to use the MB/s view
MB/s is the default view and the right default for most people. It matches the units on drive packaging and in most reviews — including every figure in our archive of real drive results — so comparisons line up without arithmetic. It is also the only sensible unit for the sequential row and for the Copy-Benchmark, where the payload per request is large and variable. If you are checking your drive against a published review, as our scoring guide recommends, stay in MB/s: that is the view the review almost certainly used.
When to use the IOPS view
Switch to IOPS when the request rate itself is the question. Drive manufacturers quote random performance in IOPS on specification sheets, so the IOPS view is the one that lets you compare a measured 4K-64Thrd result against the number on the box — the Phison E12 review above did exactly this, noting that its measured 441,299 IOPS read sat below the drive’s rated figure of up to 600,000 IOPS. IOPS is also the natural unit for server and database work, where the workload is defined by how many small operations arrive per second, and for spotting queue-depth behaviour: the jump in IOPS between the 4K row (one thread) and the 4K-64Thrd row (64 threads) shows how much parallelism the drive can turn into completed requests.
Three traps the switch creates
Trap one: comparing across units. A screenshot in IOPS pasted next to one in MB/s makes the IOPS drive look thousands of times faster. Before comparing any two results, check the unit in the grid header. Trap two: assuming the score changes. It does not — the read, write and total scores are calculated from the underlying measurements (see the score formula), and switching the display changes only how the rows are labelled. Trap three: converting the Seq row. Dividing a sequential MB/s figure by 4 KB produces a meaningless “IOPS” number, because the sequential test never issued 4 KB requests. Convert only within the rows the conversion describes.
The short version
MB/s tells you how much data moves; IOPS tells you how many requests complete. Use MB/s for everyday checks and review comparisons, IOPS for spec-sheet checks and request-rate workloads, convert 4K figures with the block-size identity above, and never compare two screenshots until you have confirmed they are showing the same unit. For the rest of the results grid, see how to read AS SSD scores.
Sharing a result? State the unit in words
Most unit confusion starts when a bare screenshot travels without its header. When you post a result — in a forum, a support thread or a marketplace listing — write the unit into your text (“4K read 54 MB/s” or “4K-64Thrd 441,299 IOPS”), and if you switched the view before taking the screenshot, say so. It takes one line, and it saves everyone who reads your result from silently comparing it against numbers in the other unit — the single most common misreading of this benchmark’s output.