It is right if VCC=5v

If VCC=5V +/- 3% then you need to correct for that.
Last time I used an ADC that used VCC and GND as reference(s). That way if VCC was off the ADC was also off by that exact amount.

 

It is right if VCC=5v

But I agree, I should have stated VCC*0.5 where VCC is the ACS712 supply voltage.

It microcontroller and ACS712 share the same supply, and the microcontroller's A/D positive reference is the positive supply, then the A/D should read 0x8000 left-justified to 16 bits when there is no current (give or take the 4% error)

 

It will not give you the value directly in amperes. You have to read the analog value with your Arduino. Then convert the value to voltage then calculate current from voltage. You also have to subtract the offset voltage. You can see a good explanation here: https://www.theengineeringprojects.com/2017/05/dc-current-sensor-acs712-arduino.html