I want total field to be filled automatically while when price and quantity entered in a form where total=price*quantity

I want the total field to be filled automatically when price and quantity are entered in a form where total=price*quantity.

class calculation(models.Model):
  price=models.IntegerField()
  quantity=models.IntegerField()
  total=models.IntegerField()

In forms.py

 class calForn(forms.ModelForm):
     class meta:
      model=calculations
      fields='__all__'