Trying to make similar kivy calculator with user input

Question

I'm just a begginer, and i try to make some calculator with user input on kivy. And i cant find why my code have issue TypeError: unsupported operand type(s) for /: 'Label' and 'int' Can someone pleas help me with some adwises?

class calculate(GridLayout):
def __init__(self, **kwargs):
    super(calculate, self).__init__(**kwargs)
    self.cols = 2
    self.rows = 5

    self.label1 = Label(text='Width in mm : ')
    self.add_widget(self.label1)

    self.user_data1 = TextInput(multiline=False)
    self.add_widget(self.user_data1)

    self.label2 = Label(text='Height in mm : ')
    self.add_widget(self.label2)

    self.user_data2 = TextInput(multiline=False)
    self.add_widget(self.user_data2)

    self.label3 = Label(text='Mass in gr : ')
    self.add_widget(self.label3)

    self.user_data3 = TextInput(multiline=False)
    self.add_widget(self.user_data3)

    self.label4 = Label(text='Mass in kg : ')
    self.add_widget(self.label4)

    self.user_data4 = TextInput(multiline=False)
    self.add_widget(self.user_data4)

    self.button = Button(text='Calculate')
    self.button.bind(on_press=self.on_user_press)
    self.add_widget(self.button)

    self.calculate = Label(text='Sheets : ')
    self.add_widget(self.calculate)

def on_user_press(self, event):
    self.calculate.number = NumericProperty(self.label4 / (self.label3 / 1000) / (self.label2 / 1000) / (self.label1 / 1000))


class Calculator(App):
    def build(self):
        return calculate()


if __name__ == "__main__":
    Calculator().run()