[Shea]

Does anyone know how I could find the weight and volume of a helium balloon?

Or, better yet, does anyone know what the weight and volume of an average helium balloon is?

[Borek]

Estimate its size, assume it is a sphere, calculate volume, multiply by helium density.

[constant thinker]

Borek is right.

V=4/3(pi)r³ <- That's volume of a sphere.

Density of helium can be found here.

The periodic table is your friend, so is wikipedia and google.

[Shea]

Wow, I was thinking about this, and I realized that it would be incredibly difficult to find the exact pressure and stuff of a balloon full of He.  I mean, with the odd shape of the balloon, and the fact that the more He you have in the balloon, the more resistance the balloon will give, I couldn't possibly ever figure it out.

But, from my estimations, and under the assumption that the balloon is only a sphere, I came up with .3953g of He.

I just guessed that the circumference is 50.8cm.  Did I screw up?

[billnotgatez]

From this site

http://www.chem.hawaii.edu/uham/lift.html

Here are some simple computations of lift of balloons. To get the real value, you would have to first weigh the uninflated balloon, any cord or other material used for closing and sealing the balloon, any nets or other lift distributing contraptions and subtract those weights.

Also a latex balloon generates some backpressure which increases the density of the gas inside and again lowers the lift. You should also take off about half a percent, to one percent of total lift for the backpressure of the inflated balloon and the resulting compression of the internal gas. This backpressure is low, maybe on the order of 5 mm of mercury, but still enough to affect lift.

[Borek]

Density of helium can be found here.

You know molar mass, you know volume at STP, you know how to divide, what do you need tables for?