The short answer: At sea level and 20°C (68°F), one liter of dry air weighs about 1.2 grams (roughly 0.0026 pounds).
Liter of air weight by type
Air is a mixture of gases, mainly nitrogen and oxygen. Its weight per liter depends on temperature, pressure, and humidity, but stays close to 1.2 grams under everyday conditions.
| Conditions (example) | Weight per liter |
|---|---|
| Dry air, 20°C, sea level | about 1.2 g |
| Cold air, 0°C, sea level | about 1.29 g |
| Hot air, 40°C, sea level | about 1.13 g |
| High altitude (thinner air) | well under 1.2 g |
What affects liter of air weight
- Temperature. Warm air expands and weighs less per liter than cold air.
- Pressure. Higher pressure packs more air into the same liter, raising weight.
- Altitude. Thinner air at high elevations weighs noticeably less.
- Humidity. Moist air is actually slightly lighter than dry air.
- Composition. The proportions of gases set air's baseline density.
How liter of air weight compares
A liter of air weighs about the same as a small paperclip, which is why we barely notice the air around us even though it has real mass.
Frequently asked questions
Why does air weigh anything at all?
Air is made of gas molecules that have mass, so a volume of it has weight. At sea level a liter weighs about 1.2 grams.
Does warm air weigh less than cold air?
Yes, warm air expands so the same liter contains fewer molecules and weighs less. This is why hot air rises above cooler air.
Is humid air heavier than dry air?
Surprisingly, humid air is slightly lighter, because water vapor molecules are less massive than the nitrogen and oxygen they displace. The difference is small but real.
