Both are correct Calculating from LMP shows your baby's actual age Ultrasound shows your baby's age according to the growth and development of organs. If you had regular periods then baby's age will be considered according to your LMP IF your cycles have been irregular then baby's age is calculated from first ultrasound scan

Go with first scan and biometry chart

12 weeks USG( NT SCAN) EDD is taken for accurate EDD. Or LMP(EDD) is also good if you have regular cycles

Calculate from 1st ultrasound done

Both to be considered

The weeks of pregnancy need to be calculated from the lmp or first ultrasound Not the ultrasound done at 32 week