Help needed in LOAD cell

Hi,

I am designing a weigh scale,
I have already selected all the components and how to interface it that also i have come to know
But i am facing one problem
the problem is i shall be interfacing the Load cell to ADC.
The ADC shall be giving 20 Bit Output data, But i Dont know how to convert this data into corresponding weight. Is there any formula for this.

Eg i Put an unknown weight and got some output as 7F082.
How will i Know this corresponds to what value in Kg or Lbs.

Please suggest something