My English is not very good
So feel free to ask, if you didn't understand what i have said
to detect free fall in adxl362, the recommended value is 600 mg which is the THRESH_INACT
there are two equations one in page 27 and other 37 to find this value

That's determined by the Measurement Range Selection (set in the Filter Control Register). If that's set to 2g and you have a resolution of 11bit, one "code" is a bit less than 1mg (2g / 2048).

Scale Factor at XOUT, YOUT, ZOUT
2 g range 1000 LSB/g
4 g range 500 LSB/g
8 g range 250 LSB/g

Consequently,
if scale is 2g: THRESH_INACT = Threshold Value [g] × Scale Factor [LSB per g] = 0.6 (600 mg) x 1000 = 600;
if scale is 4g: THRESH_INACT = Threshold Value [g] × Scale Factor [LSB per g] = 0.6 (600 mg) x 500 = 300;
if scale is 6g: THRESH_INACT = Threshold Value [g] × Scale Factor [LSB per g] = 0.6 (600 mg) x 250 = 150;