Conversion of mV to dB

KAB has a calculator for the conversion:
http://www.kabusa.com/pregain.htm

Note when using the KAB calculator that the output is based @ 5 cm/s. If your cartridge is rated @ 3.54 cm/s, you will need to multiply it by 1.41 to equate to 5 cm/s.
Just to make sure you are comparing apples to apples.

As for your phono preamp, it would help to know what speed was run to determine the mV values. For example, if running at 5 cm/s, then 0.3 mV will equate to 61 db of gain on the KAB scale. However, if using the 3.54 cm/s speed rating, then you 0.3 mV would equate to 58 db of gain. I would think it best if you ask the manufacturer this question, since we don't know what recording speed they based their numbers on.

Thank you both. I agree the KAB calculator needs to be used with caution as it does not take into consideration all of the parameters that might come into play when trying to convert different values. It appears that an accurate calculation can be done using the formula of 20 log (V1/V2) where V1 is the preamp's nominal output in terms of V rms and V2 is the sensitivity setting that is being converted. The preamp's nominal output is listed as 2V rms so let's say for the 1.4 mV setting, the gain would be 63 dB. This perfectly reflects the range provided by the manufacturer of 52-76 db from the lowest to the highest setting.

I owe credit for this to, and would like to thank, Al (Almarg), whose advice has been absolutely invaluable to me since becoming an Audiogon member. Thanks Al!