Arduino Pro Mini Voltage

I have an Arduino Pro Mini and don't know if its a 3.3V or 5V how can I tell? On the underneath there are 5 white squares and beside them they say 5V, 3.3V, 20MHz, 16MHz, 10Mhz, 8Mhz. Also which one is the correct frequency?

Thanks in advance!

Select the 5 V option and then upload the File > Examples > 01.Basics > Blink example to the Pro Mini. If the blink timing is as expected (1 s on, 1 s off), then it's the 5 V Pro Mini. If the blink timing is 2x expected (2 s on, 2 s off) then it's the 3.3 V Pro Mini.

The 5 V Pro Mini is 16 MHz. The 3.3 V Pro Mini is 8 MHz.

pert: Select the 5 V option and then upload the File > Examples > 01.Basics > Blink example to the Pro Mini. If the blink timing is as expected (1 s on, 1 s off), then it's the 5 V Pro Mini. If the blink timing is 2x expected (2 s on, 2 s off) then it's the 3.3 V Pro Mini.

The 5 V Pro Mini is 16 MHz. The 3.3 V Pro Mini is 8 MHz.

3.3V 8Mhz it is then! Thank you for the reply.

You're welcome. Enjoy! Per