I have calculated that my gas balloon's ascension rate is 13.49031149 m/s^2 WITHOUT air friction. Ignore wind and let's say ground air density is 1.2 kg/m^3 at 20 °C. The shape of the balloon will be a cylinder with rounded ends. The top end will have a 4 meter diameter so the area of that is 12.5663706 m^2. The length or height will be 14.2916666 m.