Finding helium pressure inside of balloon at 30km height with given volume

Question

I've got a aerostat with load.Total weight is 8 kg. It needs to reach altitude of 30 km. I've used Archimedes principle and II Newton's Law stating that at 30 km height the balloon will stop raising upwards thus 0 = ρ*V*g - m*g. Where ρ - air density at 30 km height, g - gravity of Earth, m - total mass. From there I've found volume at 30 km height of Helium will be V = 444,44m³. Is there a way to find what volume of gas would be needed for such balloon at launch (as balloon is flexible and inflates going up)?