Example of a new dynamic unit in kivy

dynamic_unit_kivy.py

from kivy.app import App
from kivy.app import Builder
from kivy.uix.stacklayout import StackLayout
from kivy.uix.button import Button
from kivy.properties import NumericProperty

Builder.load_string("""
<Button>:
    size_hint: None, None
    size: app.my_unit, app.my_unit*0.4
    font_size: app.my_unit*0.2
""")

class Test(App):

    my_unit = NumericProperty(100)

    def build(self):
        root_layout = StackLayout()

        resize_button = Button(text = "increase")
        resize_button.bind(on_press = self.increase_size)
        root_layout.add_widget(resize_button)

        for i in xrange(30):
            root_layout.add_widget(Button(text = "button "+str(i)))

        return root_layout

    def increase_size(self, *args):
        self.my_unit += 5
        print self.my_unit

Test().run()