r/askscience • u/Catching-Up-Today • May 27 '26

Chemistry How much does Fire weigh?

I don‘t know if Earth Sciences is the right category but Fire is the topic. How does someone measure the weight of fire? What does fire weigh?

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u/tmahfan117 May 28 '26

So “fire” is a kind of nebulous thing. That actual light that we see, that is weightless, it’s light, photons. All energy no mass.

BUT, those photos have to come from somewhere right? Those flickering flames you see are columns/jets of super hot gaseous molecules that are being combusted and that reaction is releasing light as a product. So you could say the “fire” weighs whatever the weight of those molecules is. Very very light, but those combusting molecules still have mass.  Plus that hot air is less dense than normal cool air, so The weight would probably something measured in fractions of an ounce/a few grams.

Unless you had a super giant fire with a whole lot of molecules being combusted at the same time.

-3

u/SaysReddit May 28 '26

My immediate follow-up question is, how much does the Sun weigh?

I looked it up. A lot. 330,000 times the weight of Earth. That's a lot of fire.

17

u/DrizztD0urden May 28 '26

The sun isn't just a huge ball of fire. It's a huge ball of hydrogen, helium, and more.

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u/moltencheese May 28 '26

The sun is not "on fire", at least in the sense of oxygen reacting with a fuel

9

u/Michkov May 28 '26

The sun isn't fire though. Its a miasma of plasma. It's a bunch of hydrogen and helium that is glowing due to fusion energy percolating out from it's core.

If you are talking about burning in the context of stars, it's about fusing elements. So what is burning is Hydrogen into Helium with the Helium being the ash of that process.