The *mantissa* is the fractional part of a common logarithm (that is, the base 10 logarithm), which represent the digits of the given number but not its order of magnitude.

For example, the mantissa of both \(\log_{10} 20 \approx 1.3010\) and \(\log_{10} 200 \approx 2.3010\) is \(0.3010\).

Note that the mantissa of \(\log_{10} 0.2 \approx -0.6990\) is also \(0.3010\). This is because the fractional part must always lie between \(0\) and \(1\). In this case, \(-0.6990=-1+0.3010\), so the integer part is \(-1\) while the fractional part is \(0.3010\).

See also characteristic.