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10101 in Decimal

Binary 10101 equals 21 in decimal.

10101 in all number bases

Decimal21
Hexadecimal0x15
Binary0001 0101
Octal25

How 10101 converts from binary to decimal

Multiply each digit by 2 raised to its position (starting at 0 from the right), then add the results:

1× 24 = 1 × 16 = 16
0× 23 = 0 × 8 = 0
1× 22 = 1 × 4 = 4
0× 21 = 0 × 2 = 0
1× 20 = 1 × 1 = 1

Sum: 21