Welcome to the community, @hhfoffice! You could do this as outlined in the image shared below:
In the survey tab of your XLSForm:
Data entry screen as seen in Enketo:
Reference XLSForm:
Calculate BMI.xlsx (9.1 KB)
Welcome to the community, @hhfoffice! You could do this as outlined in the image shared below:
Calculate BMI.xlsx (9.1 KB)