Balloons are measured according to its weight but not by its size. The burst altitude does not depend on the size of the balloon itself. There are more critical factors playing a role like humidity, pressure, temperature and the balloon manufacturing quality that greatly affect the final bursting diameter.
The heavier the balloon is, the heavier the payloads they can carry and the higher altitude it can reach. While a 600gr balloon is capable of reaching up to 25 km high a 1600gr balloon will reach altitudes above 35 km.
In general, the weight of the balloon should be large enough to meet the requirements of the mission, otherwise the target altitude would not be accomplished. As an example, if the balloon is too large a lot of helium will be wasted and one will be spending extra money to send a payload up to the stratosphere.
Another important factor to take into account is the balloon’s neck size. The neck size should be greater enough to ensure there is friction between it and the inflation nozzle. If we don’t meet this requirement, the chance to slip off during the inflation process increases.
A big sized and reinforced neck also helps while the balloon is in its ascending phase not weakening its overall endurance and keeping the helium inside it at a higher altitudes.