How to calculate IOPS per disk

There are some numbers already provided by vendors

SAS (15K RPM) à 175 IOPS

SATA (7.2K RPM) à 75 IOPS

Now how do they come up with these numbers?

The formula is

Estimated IOPS = 1 / ((Seek time/1000) + (Latency / 1000))

Now let’s put this formula into perspective

Seagate Cheetah 15k hard drive

http://www.seagate.com/www/en-us/products/enterprise-hard-drives/cheetah-15k#tTabContentSpecifications

Estimated IOPS = 1 / ((average read seek time + averagewrite seek time)/2)/1000 + (Average latency / 1000)

Estimated IOPS = 1 / ((3.65 / 1000) + (2.0 / 1000) = 1 /(0.00365) + (0.002) = 176.9911

Answer is ~ 175 IOPS