# another propane question **URL:** \ **Category:** Factual Questions\ **Created:** [May 1, 2002, 4:02pm UTC](https://boards.straightdope.com/t/another-propane-question/106670 "2002-05-01T16:02:53Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![SlickRoenick](https://avatars.discourse-cdn.com/v4/letter/s/e68b1a/32.png) [@SlickRoenick](https://boards.straightdope.com/u/SlickRoenick)\ **Post date:** [May 1, 2002, 4:02pm UTC](https://boards.straightdope.com/t/another-propane-question/106670/1 "2002-05-01T16:02:53Z")
How many PSI goes into a standard 20lbs propane tank? What about 100lb tanks? ---
**Author:** ![scotth](https://avatars.discourse-cdn.com/v4/letter/s/b9e5f3/32.png) [@scotth](https://boards.straightdope.com/u/scotth)\ **Post date:** [May 1, 2002, 4:31pm UTC](https://boards.straightdope.com/t/another-propane-question/106670/2 "2002-05-01T16:31:15Z")
The answer will be the same regardless of the tank size. Propane tanks hold liquid propane. As long as any liquid is left in the tank, the pressure will be determined by temperature. What causes the pressure is the propane trying to boil. The propane will in fact boil until the rise in pressure raises its boiling point to the ambient temp. Temperature: -20ºF - 10 psi Temperature: 0ºF - 24 psi Temperature: 20ºF - 41 psi Temperature: 40ºF - 63 psi Temperature: 70ºF - 109 psi Temperature: 100ºF - 172 psi at -44ºF and below, propane will stay liquid uncontained at normal atmospheric pressure. ---
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [May 1, 2002, 6:51pm UTC](https://boards.straightdope.com/t/another-propane-question/106670/3 "2002-05-01T18:51:53Z")
add to that that the propane liquid cools as it is used (due to it evaporating in the tank, and that is why propane is a bad fuel choice for stuff like winter hiking. ---
**Author:** ![SlickRoenick](https://avatars.discourse-cdn.com/v4/letter/s/e68b1a/32.png) [@SlickRoenick](https://boards.straightdope.com/u/SlickRoenick)\ **Post date:** [May 2, 2002, 2:08am UTC](https://boards.straightdope.com/t/another-propane-question/106670/4 "2002-05-02T02:08:35Z")
That’s nice with the temperatures, but I still don’t know the psi inside. What would the temperature be inside the tank and how high is the psi? ---
**Author:** ![choosybeggar](https://avatars.discourse-cdn.com/v4/letter/c/8c91f0/32.png) [@choosybeggar](https://boards.straightdope.com/u/choosybeggar)\ **Post date:** [May 2, 2002, 2:20am UTC](https://boards.straightdope.com/t/another-propane-question/106670/5 "2002-05-02T02:20:23Z")
> [@](#): > > That’s nice with the temperatures, but I still don’t know the psi inside. What would the temperature be inside the tank and how high is the psi? The temp inside the tank (provided no cooling effects from removing propane) is the same as the temp outside the tank. It’s ambient. Use ambient temp to calculate the pressure inside using **scotth’s** handy table. ---
**Author:** ![GusNSpot](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gusnspot/32/436_2.png) [@GusNSpot](https://boards.straightdope.com/u/GusNSpot)\ **Post date:** [May 2, 2002, 6:10am UTC](https://boards.straightdope.com/t/another-propane-question/106670/6 "2002-05-02T06:10:46Z")
Why hot air ballons have heated blankies they wrap their tanks in. Sure want nuff pressure to make the burner burn ya know. ---
**Author:** ![scotth](https://avatars.discourse-cdn.com/v4/letter/s/b9e5f3/32.png) [@scotth](https://boards.straightdope.com/u/scotth)\ **Post date:** [May 2, 2002, 1:50pm UTC](https://boards.straightdope.com/t/another-propane-question/106670/7 "2002-05-02T13:50:26Z")
> [@](#): > > \*Originally posted by Muldoon III \* > \*\*That’s nice with the temperatures, but I still don’t know the psi inside. What would the temperature be inside the tank and how high is the psi? \*\* Just to make sure this isn’t what is messing you up: Although, the measurement for capacity of a propane tank is measured in lbs, it has nothing to do with the pressure in the tank. It really is a measure of the weight of the fuel inside. It could just as well be measured in gallons. That would probably make it clearer. The reason propane isn’t usually measured in gallons, is that propane expands and contracts quite a bit due to temp. A gallon at 30F would be more fuel than a gallon at 75F. A pound, or a kilogram, of propane may take up more or less volume at different temps, but is still the same amount of fuel. If you are not adding or removing fuel from the tank, the temperature of the interior of the tank will become the same as the outside of the tank. The pressure inside the tank will then be determined by the chart I posted above as long as there is ANY liquid propane left in the tank. A completely full, half full, and nearly empty tank will all have the same static pressure. This will be true for any tank, regardless of size.