Once the ADC completes a conversion, the ADC Interrupt Flag bit in the ADC Control and Status A register (ADCSRA.ADIF) will be set to '1' and the 10-bit result will be available in the ADCH and ADCL registers.
For single conversion, the result is:
where VIN represents the analog input voltage and VREF represents the selected reference voltage. '0x000' represents GND and '0x3FF' represents the selected reference voltage minus one LSB.