Calibration of different range CT (1000A/5A) ,(1500A/5A) to get accurate current

Hello, In my project i am using ADS1256 sensor with RPI for energy meter application, i can able to read the voltage value and now i am trying to read the current for different CT first of all is it possible to use same firmware/code to read the CT off-course with calibration.
and now i have connected CT with range(1000A/5A) to ADS1256 sensor the load consumes around 1.5A i don’t have large current consuming load. the problem actually the calculation for match with actual current consumed by load . The CT have inbuilt burden resistor since the output will be in voltage only i mean ADC raw value and its around 0.8v for 1000A/5A so how to match with actual current and please let me know is it possible to calibrate different CT’s with same firmware or will it work for that.
Thank You.