What Minimum Value Can I Measure With ACS712 30A Current Sensor?
That model has a sensitivity of 66mV/A which means for every 1A of current passing through it outputs 66mV.
The Arduino's ADC when running at 5V has a resolution of (5/1024) 4.88mV per LSB.
That means that 4.88/66 gives you 0.074 - or 74mA per LSB.
Since 1LSB is considered to be in the noise area of the signal you can expect the minimum usable value to be double that - 148mA
Which is pretty useless for measuring currents in the mA range.
You would get better results with the 5A variant, but still not great.