I don’t know of any utility that claims to measure the rotation rate. Maybe someone else could help you with that. However, I believe those utilities that report the RPM simply do so by looking at the 512-byte data block returned by the drive in response to an ATA Identify Device command.
See section 7.16.4 (page 131 of PDF) of the following document.
Working Draft AT Attachment 8 - ATA/ATAPI Command Set (ATA8-ACS):
Word 217 reports the “Nominal media rotation rate”.
In this example …
… the RPM is 0x170C, which is 5900 RPM.
One way you could estimate the RPM is by examining the spread of data points in the graph of access time in HD Tune’s read benchmark.
For example, in the following graph you can see that, at the 450GB mark, the band of data points are about 8 msec wide.
The total access time is the time required to seek to the target cylinder, plus the time required for the target sector to pass under the read/write head. The latter time component can vary from 0 to one full revolution. Therefore this “rotational latency” will be seen as a band whose width is 8.33 ms in the case of a 7200 RPM drive, and about 11ms for a 5400 RPM drive.