The weight or mass of a cotton ball varies because cotton balls come in different sizes and densities. However, many cotton balls have an estimated mass close to 0.5 grams, according to measurements obtained from Amazon product information.
One can calculate an upper bound for the average mass or weight of a cotton ball by dividing the total package weight by the number of cotton balls. Taking several example packages of different types of cotton balls available from Amazon, the average weight of a cotton ball ranges up to 0.5 grams.
Using this calculation, the estimated shipping weight of a jumbo cotton ball ranges up to 0.453 grams. A medium cotton ball weighs an estimated 0.408 grams, and a medium small cotton ball weighs about 0.566.
The actual mass per cotton ball in these examples is slightly less than the calculated value for the upper bound because the weight of the packaging containing the cotton balls is unknown and can't be subtracted from the shipping weight.