The long and short scales are two of several naming systems for integer powers of ten which use some of the same terms for different magnitudes.

Some languages, particularly in East Asia and South Asia, have large number naming systems that are different from both the long and short scales, such as Chinese, Japanese or Korean numerals, and the Indian numbering system.

Much of the remainder of the world adopted either the short scale or the long scale for everyday counting powers of ten. Countries with usage of the long scale include most countries in continental Europe and most that are French-speaking, German-speaking, Spanish-speaking and Portuguese-speaking countries (except Brazil). Usage of the short scale is found in most English-speaking countries and most Arabic-speaking countries.

For whole numbers smaller than 1,000,000,000 (10⁹), such as one thousand or one million, the two scales are identical. For larger numbers, starting with 10⁹, the two systems differ. For identical names, the long scale proceeds by powers of one million, whereas the short scale proceeds by powers of one thousand. For example, in the short scale, "one billion" means one thousand millions (1,000,000,000), whereas in the long scale, it means one million millions (1,000,000,000,000). For interleaved values, the long scale system employs additional terms, typically substituting the word ending -ion for -iard. For example the short scale billion is called milliard in the long scale, the short scale trillion is called billion in the long scale, the short scale quadrillion is called billiard in the long scale, and so forth.

To avoid confusion resulting from the coexistence of the two terms, the International System of Units (SI) recommends using the metric prefix to indicate orders of magnitude, associated with physical quantities.