Disk IOPS Calculator
Calculate achievable disk IOPS from rotational speed, seek time and queue depth.
About Disk IOPS Calculator
For mechanical hard drives, each random I/O operation must wait for the read/write head to seek to the correct track, then wait for the platter to rotate the target sector under the head (rotational latency), then transfer the data — so IOPS is simply 1000ms divided by the sum of those three latencies. Solid-state drives have no moving parts and instead are limited by controller and NAND access latency per operation; because SSDs can service many requests in parallel, total achievable IOPS scales roughly linearly with queue depth up to the device's internal parallelism limit, so this calculator multiplies single-operation IOPS by the queue depth.
Formulas
HDD random IOPS
IOPS = 1000 / (seek_time_ms + rotational_latency_ms + transfer_time_ms)
- t_{seek}
- average seek time in ms
- t_{rot}
- average rotational latency in ms
- t_{xfer}
- data transfer time in ms
SSD IOPS with queue depth
IOPS = queue_depth × (1000 / latency_ms)
- Q
- queue depth
- L
- latency per operation in ms
Worked example
With the default values below, Disk IOPS Calculator returns Estimated IOPS of 320,000.0. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Disk Typeone of HDD — 7200 RPM, HDD — 10000 RPM, HDD — 15000 RPM, SSD
- SSD
- Transfer Time (HDD only)minimum 0 ms
- 0.5 ms
- SSD Latency per Operation (SSD only)minimum 1 µs
- 100 µs
- Queue Depth (SSD only)minimum 1
- 32
Results
- Estimated IOPS
- 320,000.0
- Disk Profile
- SSD
- Average Access Latency
- 0.100 ms
- Single-Queue IOPS (SSD only)
- 10,000
Step by step
- 1Values used
- 2HDD random IOPS
- 3SSD IOPS with queue depth
- 4Estimated IOPS= 320,000.0
- 5Disk Profile= SSD
- 6Average Access Latency= 0.100 ms
- 7Single-Queue IOPS (SSD only)= 10,000
Assumptions and limits
- The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
Why does queue depth matter so much for SSD IOPS but not HDD IOPS?
An HDD's mechanical head can only be in one physical location at a time, so queuing more requests mostly just adds waiting time rather than parallel throughput. SSDs have multiple NAND channels and no moving parts, so many operations genuinely execute in parallel, and total IOPS scales with queue depth until the controller's parallelism is saturated.
What is a typical rotational latency for a 7200 RPM drive?
Average rotational latency is half a full rotation: for 7200 RPM (120 revolutions/second), one rotation takes 8.33ms, so average latency is about 4.17ms — the value used as the default in this calculator.
Why is real-world IOPS often lower than this calculation?
This model estimates raw random-access IOPS from hardware latency alone. Real workloads also contend with filesystem overhead, RAID write penalties, controller cache behavior and mixed read/write patterns, all of which typically reduce effective IOPS below the theoretical hardware ceiling.