How do you value AspectRatio?

So I am trying to use AspectRatio on my GUI but it says the value is a float and I can't find any articles on the wiki other then the directed link to numbers which doesn't specify it...

--Variables
local StarterGui = script.Parent
local UI = Instance.new('UIAspectRatioConstraint')
local image = Instance.new('ImageLabel')

--Parents
image.Parent = screenGui
UI.Parent = image

--???
UI.AspectRatio = ?

for more understanding I'm trying to find out what a float is if anyone could help.

Edit: When I use Vector2 and a Integer that's positive it errors and says I need a positive value :/

thx, RoButCantBlox