Quick start
- Type the value, such as 255 or FF or 11111111.
- Set "From base" to the base it is written in: 2, 8, 10, 16 or anything up to 36.
- Optionally enter one more base to see.
From any base to decimal
Multiply each digit by the base raised to its position, counting from 0 on the right, and add. Binary 1011 = 1×8 + 0×4 + 1×2 + 1×1 = 11. Hex 2F = 2×16 + 15 = 47.
From decimal to any base
Divide by the new base repeatedly and keep the remainders. Read them from the last to the first. 47 ÷ 2 gives remainders 1, 1, 1, 1, 0, 1, so 47 in binary is 101111.
Digits beyond 9
Bases above 10 need extra digit symbols, so letters are used: A = 10, B = 11, up to Z = 35. That is why hexadecimal uses 0–9 and A–F.
Where you see each base
- Binary (2): how computers store data.
- Octal (8): Unix file permissions, such as 755.
- Hexadecimal (16): web colours like #1E90FF, and memory addresses.
Common questions
What is 255 in hex?
FF. In binary it is 11111111.
Are lowercase letters OK?
Yes. ff and FF are read the same.
Why is base 36 the limit?
10 digits plus 26 letters gives 36 symbols.