What is 11111111 in decimal?

Binary 11111111 equals 255 in decimal (the value 255, the largest number that fits in one byte).

Why are binary and decimal used?

Binary (base 2) is how computers store data, as bits that are either 0 or 1. Decimal (base 10) is the everyday number system.

Binary to Decimal

Quickly convert binary numbers to decimal format accurately, helping students, programmers, and engineers understand numeric values, perform calculations, and debug code efficiently.

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Updated Sep 2026

In short

To convert binary to decimal, multiply each binary digit by 2 raised to its position (starting at 0 on the right) and add the results. For example, 101101 = 1×2^5 + 0×2^4 + 1×2^3 + 1×2^2 + 0×2^1 + 1×2^0 = 45.

How it works

Binary counts in base 2, decimal counts in base 10. Converting means rewriting the same quantity with a different set of digits — the value never changes, only how it is written.

Number the digits from the right, starting at 0.
Multiply each digit by 2 raised to the power of its position.
Add the results — that total is the decimal value.

The reverse conversion is Decimal to Binary, which also handles every other base pair.

Examples

Worked examples, digit by digit:

1010 (binary) = 1×2³ + 0×2² + 1×2¹ + 0×2⁰ = 10 (decimal)
10101 (binary) = 1×2⁴ + 0×2³ + 1×2² + 0×2¹ + 1×2⁰ = 21 (decimal)
11111111 (binary) = 1×2⁷ + 1×2⁶ + 1×2⁵ + 1×2⁴ + 1×2³ + 1×2² + 1×2¹ + 1×2⁰ = 255 (decimal)

Common values in every base
Decimal	Binary	Octal	Hexadecimal
0	0	0	0
1	1	1	1
2	10	2	2
4	100	4	4
8	1000	10	8
10	1010	12	A
15	1111	17	F
16	10000	20	10
32	100000	40	20
64	1000000	100	40
100	1100100	144	64
255	11111111	377	FF

Binary to Decimal: frequently asked questions

How do I convert binary to decimal?: Multiply each binary digit by 2 raised to its position (starting at 0 on the right) and add the results. For example, 101101 = 1×2^5 + 0×2^4 + 1×2^3 + 1×2^2 + 0×2^1 + 1×2^0 = 45. The converter above does this instantly for any value.
What is 11111111 in decimal?: Binary 11111111 equals 255 in decimal (the value 255, the largest number that fits in one byte).
Why are binary and decimal used?: Binary (base 2) is how computers store data, as bits that are either 0 or 1. Decimal (base 10) is the everyday number system.