A rubber band can only stretch as far as its elastic limit, which is dependent upon its thickness and quality. When stretched beyond this limit, the rubber band breaks.
To determine the elasticity of a rubber band, determine the amount of weight in grams required to stretch it to its elastic limit. Then, convert the grams to Newtons, which is a measure of elastic force. The basis of conversion is 9.8 Newtons per 1,000 grams. For example, if 500 grams of weight is required to stretch a rubber band to its limit, then it has an elasticity of 4.9 Newtons.