# How many pounds are in a gallon?

1. Oct 1, 2005

### darkwolf

How many pounds are in a gallon? (I need exact amount). What is the Formula any and all for gallons to pounds.
my e-mail is darkravewolf@sbcglobal.net

2. Oct 1, 2005

### Danger

That entirely depends upon what it is a gallon of. Also, you need to specify whether it's a real gallon or a Yank gallon.

3. Oct 1, 2005

### FredGarvin

You need the density or specific gravity of what you are trying to calculate the volume of. There is no direct conversion from weight to volume.

4. Oct 2, 2005

### darkwolf

i need to know the poundage of 90 us water gallons

5. Oct 2, 2005

### darkwolf

as well as how much weight can a 2x4 hold up

6. Oct 2, 2005

### Danger

The first is easy if you go with pure water at room temperature; mineral content and temperature differences vary it. One cc of water weighs one gram. Just convert your units to find how many cc's there are in a gallon (the information is readily available), and then convert your result from grams to pounds.
The second question is another that requires far more information to answer. An oak 2x4 is a lot stronger than a balsa one. It also matters which way it's oriented. Lastly, there are almost always flaws of some type, be it knots or warpage or whatever.

7. Oct 2, 2005

### rcgldr

Weight of 1 US gallon of water is 8.33 pounds. 90 gallons would weigh 749.7 pounds.

As far as how much weight a 2x4 can hold, it depends on how the 2x4 is supporting weight as well as the material involved, but you can probably assume construction grade pine. Note that a 2x4 is not 2 inches by 4 inches either.

8. Oct 2, 2005

### FredGarvin

The 2x4's allowable load will also greatly depend on it's orientation, i.e. it's area moment of inertia.

Wood, like most composites, is a bit of a tough material when dealing with calculations of this type. There are so many variables that can effect it's true strength that you really have to be careful. Plus, it is not an unreasonable assumption that the material is non-homogeneous, which most standard derived equations like $$\sigma = \frac{M c}{I}$$ are based on.

According to Mark's Handbook, it looks like the range for elastic modulus of a standard kind of pine with a 12% moisture content is between 1200 and 1400 ksi (Table 6.7.2, pg. 6-115). Personally, I would include a healthy safety margin in that if this calculation is going to be for something around people or can cause damage.

Last edited: Oct 2, 2005