How would you suspend a character in the air using a BodyThrust?

At the moment I am working on a jetpack using BodyMovers. I can't seem to find an equation or anything on how much force is needed to suspend the character in the air. I looked on wiki and asked a lot of people but no one seems to be able to figure it out.

Heres the script I made to do this. Everything works fine, I just need to know how much force is needed.

				if Key == 5 then
					if Up == false then
						Up = true
						local UpThrust = Instance.new("BodyThrust",Character.HumanoidRootPart)
						UpThrust.Name = "Up"
						UpThrust.Location = Vector3.new(0,0,0)
						UpThrust.Force = Vector3.new(0,3000,0)
					else
						local UpThrust = Character.HumanoidRootPart:FindFirstChild("Up")
						if UpThrust then
							local mass = 0
    						for _,v in next, Character:GetDescendants() do
     					    	if v:IsA("BasePart") then mass = mass + v:GetMass() end
   							end
							UpThrust.Force = Vector3.new(0,workspace.Gravity*mass,0)
						end
						print("Suspending Character")
						Up = false
					end
				end