A typical balloon is about 55 feet across and 60 to 80 feet tall. They are categorized by how much air the envelope can contain. a common sizes is the AX-7, with an envelope volume of 77,000 cubic feet. This is the most widely flown model because it can be easily handled by a crew of three to four people.

The volume of air inside a hot air balloon varies by the size of the "envelope," but a standard commercial balloon used for sightseeing (categorized as an AX-7 or AX-8) typically holds between 77,000 and 105,000 cubic feet of air. To put that in perspective, that is roughly the same volume as 1,500 to 2,000 standard refrigerators. For larger groups of 12 to 20 people, the envelopes can reach volumes of 300,000 cubic feet or more. In 2026, modern balloons are engineered with heat-resistant nylon or polyester fabrics to trap this massive volume of air. The "lift" is created because the air inside the balloon is heated to roughly 100°C (212°F), making it significantly less dense than the cooler ambient air outside. The weight of the air being displaced is what allows the balloon—and its several hundred pounds of basket, fuel, and passengers—to rise gracefully into the sky.