This little JS plugin will help you calculate ms or hz values for normal, dotted and triplet note values:

It can also divide note values by user chosen subdivision value
Operation modes:
• Project BPM: It uses the current tempo
- tempo markers are taken into account so watch out where your edit cursor is
- playback rate is also taken into account
• Free mode: You can set arbitrary BPM in Calculator
Version 1.2
-added an option to divide note values by user chosen subdivision
-free mode can now be used even if audio device is closed and it refreshes instantly no matter the size of buffer
How to install
Copy the file to C:\Users\Breeder\AppData\Roaming\REAPER\Effects
You can of course put it in any folder you like. I keep it in Utility