GUI Frame size depending on IntValue?

I've been trying to make a StatsGui - Hunger, Thirst and Health. The values work fine I'm just wondering how you'd resize the frame equivilent to the value? (If Thirst = 500 then the frame would be half of the GUIs size)

plr.Character:WaitForChild("Humanoid").Running:connect(speed)
if speed > 0 then
    game.Players.LocalPlayer.Thirst.Value = game.Players.LocalPlayer.Thirst.Value - math.random(1,8)
    script.Parent.Thirst.Size = UDim2.new(0,  ____  ,0,40) -- Duno what to put in this bit...
end

The main GUI is sized: {0, 400},{0, 175} And the bar im trying to resize is set default to: {0, 160},{0, 40} - The bit that would change by the IntValue being the 160 with it's max size being 320. And the maximum value of the IntValue that should be changing the size of this, is 1000...

Any help would be much appreciated :)