The ADC Pi uses resistor voltage dividers on each input using 10k and 6K8 values to reduce inputs down to a voltage suitable for the ADC chip. By default the input voltage can be a maximum of 5.06V but this can be increased by adding a resistor in series with the input as shown on the illustration.
This tool calculates the resistance for R1 and a multiplier required for our ADC Pi code libraries. You can use this calculator to increase the voltage range of the ADC Pi.
5V to 100V