Converting binary to decimal means turning a base-2 number into the base-10 number system people use every day, and it works entirely through place values, no ASCII table needed.
This is a different kind of conversion from turning binary into letters: here the binary number represents a quantity, not a character, so the math works differently under the hood.
The Place-Value Method
In an 8-bit binary number, each position stands for a power of two: 128, 64, 32, 16, 8, 4, 2, and 1, reading left to right. A decimal value only counts a position if that digit is a 1.
Step by Step
Write the power-of-two value above every digit in the binary number. Add together only the values sitting above a 1. Ignore every position where the digit is a 0. The total is the decimal number.
A Worked Example
Take 01011010. The 1s sit in the 64, 16, 8, and 2 positions. Adding 64 plus 16 plus 8 plus 2 gives 90, so 01011010 equals 90 in decimal.
Going the Other Direction
Converting decimal back to binary works in reverse: subtract the largest power of two that fits, mark that position as 1, and repeat with what is left until nothing remains.
Practice More
For more worked examples at different bit lengths, see our binary to decimal practice guide and our breakdown of common binary number conversions like 256 and 128. For the full picture of how the number system works, start with what binary code is and how it works.