How many (helium filled) balloons do I need to lift 300 grams?

Take a balloon Keep adding weighted material (say, water) at a constant measure; say, half a cup at a time, or 50 gr at a time. Continue, until it is still at the height you want. Then you know the lifting capabilities of each balloon. read more

One balloon that is 30 meters (about 100 feet) in diameter displaces 14,137,000 liters, so it can lift 14,000 kilograms (about 31,000 pounds) -- this is roughly the size of a large blimp. For a baby, you would need fewer than 4,000 balloons. read more

According to Broadway Party, one 9″ balloon requires about .112 cubic feet to fill, and can lift about .13 ounces, or 3.685 grams. Using this information, we can figure that 81.4111261872 cubic feet of helium is required to lift your payload, because 300g/3.685g=81.4111261872ft^3. read more