You can set the width and height of widgets in guizero.

Widgets are sized by either pixels or characters depending on the widget and what it contains.

Some widgets size can also be set to "fill" where it will use up all of the available space.

from guizero import App, PushButton, Slider, ListBox

app = App()

# A PushButton's size is noted in characters
button = PushButton(app, width=30, height=5)

# A Slider's size is noted in pixels
slider = Slider(app, width=300, height=30)

# Some widgets such as ListBox can also be told to fill all the available space
listbox = ListBox(app, width="fill", height="fill")

Widget Characters or Pixels Fill Notes
Box Pixels Yes If a Box is sized in Pixels, both width and height must be specified.
ButtonGroup Characters Yes The height of a ButtonGroup must divide by the number of buttons in it
CheckBox Characters Yes
Combo Characters Yes
ListBox Pixels Yes
Picture Pixels No See Images for more information
PushButton Characters Yes
PushButton with image Pixels No PushButton's which have images are sized in pixels
Slider Pixels Yes
Text Characters Yes
TextBox Characters Yes Only a TextBox's width can be set
Waffle Pixels No