Each letter in the alefbet has a numerical value. These values can be used to write numbers, as the Romans used some of their letters (I, V, X, L, C, M) to represent numbers. The table at right shows each letter with its corresponding numerical value. Note that final letters have the same value as their non-final counterparts.

The numerical value of a word is determined by adding up the values of each letter. The order of the letters is irrelevant to their value: the number 11 could be written as Yod-Alef, Alef-Yod, Heh-Vav, Dalet-Dalet-Gimmel or many other ways. Ordinarily, however, numbers are written with the smallest possible number of letters and with the largest number first (that is, to the right). The number 11 would be written Yod-Alef, the number 12 would be Yod-Bet, the number 21 would be Kaf-Alef, the number 611 would be Tav-Resh-Yod-Alef, etc. The only significant exception to this pattern is the numbers 15 and 16, which if rendered as 10+5 or 10+6 would be a name of G-d, so they are normally written Tet-Vav (9+6) and Tet-Zayin (9+7).

Because of this system of assigning numerical values to letters, every word has a numerical value. For example, the word Torah (Tav-Vav-Resh-He) has the numerical value 611 (400+6+200+5). There is an entire discipline of Jewish mysticism known as Gematria that is devoted to finding hidden meanings in the numerical values of words. For example, the number 18 is very significant, because it is the numerical value of the word Chai, meaning life. Donations to Jewish charities are routinely made in denominations of 18 for that reason.

I have received several e-mails pointing out that the numerical value of Vav (often transliterated as W) is 6, and therefore WWW has the numerical value of 666! It's an amusing notion, but Hebrew numbers just don't work that way. In Hebrew numerals, the position of the letter/digit is irrelevant; the letters are simply added up to determine the value. To say that Vav-Vav-Vav is six hundred and sixty-six would be like saying that the Roman numeral III is one hundred and eleven. The numerical value of Vav-Vav-Vav in Hebrew would be 6+6+6=18, so WWW is equivalent to life! (It is also worth noting that the significance of the number 666 is a part of Christian numerology, and has no basis that I know of in Jewish thought).