Number of speakers of English
The number of speakers of English worldwide is not as easy to calculate as might be imagined. Not all countries have accurate census data, if they do they don't necessarily count the languages spoken by their citizens and finally one may ask what it means to "speak" English.
Whatever the actual figures it is possible that they are overestimated in the (English speaking) public's mind. A Harris poll found that on average, adult Americans believe that just over half (52%) of the whole world's population speak English. Harris maintains that the real number is probably closer to 20% at maximum.