2.6 t5,730 lb
The hot air inside a typical 2,800 m³ (100,000 cu ft) hot air balloon weighs about 2.6 tonnes (5,700 lb). The same space filled with outside air at 20 °C would weigh about 3.4 tonnes, and that difference, roughly 700 to 870 kg, is what lifts the envelope, basket, burners and passengers.
| Hot air in a Cameron Z-750, at 99 °C21,238 m³, the largest on Cameron’s type certificate | 20.1 t44,300 lb |
|---|---|
| Cool outside air filling a 2,800 m³ envelopeAt 20 °C, sea level | 3.41 t7,520 lb |
| Hot air in a 2,800 m³ balloon, at 99 °CGives 723 kg of lift | 2.69 t5,920 lb |
| Hot air in a 2,800 m³ balloon, at 120 °CThe hottest allowed; 867 kg of lift | 2.54 t5,600 lb |
| Hot air in a Colt 17A, at 99 °C498 m³, the smallest on the same certificate | 472 kg1,040 lb |
Hot air is lighter than cold air, but it is not weightless. At 20 °C and sea level, air weighs about 1.204 kg per cubic metre. Heated to 99 °C it weighs 0.949 kg per cubic metre, and at 120 °C 0.898 kg. A balloon is open at the bottom, so as the air inside heats and expands, some of it spills out and what is left is thinner.
The most-used balloon size is about 2,800 m³ (99,000 cu ft). Filled with air at 99 °C, it holds 2,686 kg of air; at 120 °C, 2,542 kg. Our 2.6 tonnes sits between the two, for air at about 110 °C. Filled with 20 °C outside air instead, the same envelope would hold 3,410 kg.
The lift is the weight of the outside air the envelope pushes aside, minus the weight of the hot air inside. For 2,800 m³ heated to 99 °C that is 723.5 kg (1,595 lb); at 120 °C it rises to 867.3 kg (1,912 lb). Everything has to fit inside it: the envelope, the basket, the burners, the propane and the people.
Pilots cannot simply keep heating. Cameron’s type certificate says the envelope temperature must not exceed 120 °C (250 °F), to protect the nylon fabric. Flown within that limit, an envelope typically lasts 400 to 500 hours before the fabric needs replacing. For a Cameron 100,000 cu ft balloon the certified maximum take-off mass is 907 kg, envelope and all. A balloon this size carries 3 to 5 people.
Cameron’s type certificate, which also covers its Colt and Thunder brands, runs from the Colt 17A at 17,600 cu ft (498 m³), with a maximum take-off mass of just 160 kg, up to the Z-750 at 750,000 cu ft (21,238 m³) and 5,103 kg. Heated to 99 °C, the air in the small one weighs about 470 kg, and the air in the Z-750 about 20 tonnes. Sightseeing balloons of up to 17,000 m³ can carry well over two dozen passengers.
The envelope itself is light by comparison. Cameron lists its Z-105, about 2,974 m³ and 64 ft (20 m) tall, at a standard weight of 249 lb (113 kg), less than a twentieth of the air it holds.
In a typical 2,800 m³ balloon, about 2.5 to 2.7 tonnes (5,600 to 5,900 lb), depending on how hot it is. We use 2.6 tonnes. The same volume of outside air at 20 °C weighs about 3.4 tonnes.
A 2,800 m³ balloon heated to 99 °C gives about 723 kg (1,595 lb) of lift, and about 867 kg (1,912 lb) at the 120 °C limit. That has to carry the envelope, basket, burners, fuel and passengers.
Roughly 100 °C: at 99 °C a typical 2,800 m³ balloon already gives about 723 kg of lift. Cameron’s type certificate says the envelope must never go above 120 °C (250 °F).
The most common size is about 2,800 m³ (99,000 cu ft), enough for 3 to 5 people. Cameron’s 105,000 cu ft Z-105 stands about 64 ft (20 m) tall.
Because the hot air inside weighs less than the cooler air it pushes aside. For a 2,800 m³ balloon at 99 °C, the difference is about 723 kg, and the balloon rises when that is more than the balloon and its load.
Last checked October 4, 2026.
