useful info from another board:
1 Liter or 1000cc (or ml) equals 1 kg or about 2.2 lbs. We're going to use 1 foot of showtime's 3.5" diameter noodle. Converting this to metric we use 1"=2.54cm. So, the noodle is 30.48cm long by 8.89cm in diameter.
Here goes: volume of a cylinder=pi(r)(r)(length)or 22/7 X 4.445cm X 4.445cm X 30.48cm = 1892.7cc or 1.89L
Converting the weight of 1.89L of water back to pounds is 1.89kg X 2.2=4.16 lbs. This does not take into account the hole going down the length of the noodle! In other words, the noodle will actually support a little less than 4.16 lbs!
So.......1 foot of 3.5" diameter pool noodle should float about a 4lb piece of metal on top of the noodle.