# Number — Number encoding

> The JavaScript Number type is a double-precision 64-bit binary format IEEE 754 value, like double in Java or C#.

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- Updated: `2026-08-16T09:32:14.507132+00:00`
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## Knowledge

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The JavaScript Number type is a double-precision 64-bit binary format IEEE 754 value, like double in Java or C#. This means it can represent fractional values, but there are some limits to the stored number's magnitude and precision. Very briefly, an IEEE 754 double-precision number uses 64 bits to represent 3 parts

1 bit for the _sign_ (positive or negative) 11 bits for the _exponent_ (-1022 to 1023) 52 bits for the _mantissa_ (representing a number between 0 and 1)

The mantissa (also called _significand_) is the part of the number representing the actual value (significant digits). The exponent is the power of 2 that the mantissa should be multiplied by. Thinking about it as scientific notation

Number=(−1)sign⋅(1+mantissa)⋅2exponent\text{Number} = ({-1})^{\text{sign}} \cdot (1 + \text{mantissa}) \cdot 2^{\text{exponent}}

The mantissa is stored with 52 bits, interpreted as digits after 1.… in a binary fractional number. Therefore, the mantissa's precision is 2-52 (obtainable via {{jsxref("Number.EPSILON")}}), or about 15 to 17 significant decimal digits; arithmetic above that level of precision is subject to rounding.

The largest value a number can hold is 21023 × (2 - 2-52) (with the exponent being 1023 and the mantissa being 0.1111… in base 2), which is obtainable via {{jsxref("Number.MAX_VALUE")}}. Values higher than that are replaced with the special number constant {{jsxref("Infinity")}}.

Integers can only be represented without loss of precision in the range -253 + 1 to 253 - 1, inclusive (obtainable via {{jsxref("Number.MIN_SAFE_INTEGER")}} and {{jsxref("Number.MAX_SAFE_INTEGER")}}), because the mantissa can only hold 53 bits (including the leading 1).

More details on this are described in the ECMAScript standard.

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