What is the highest decimal value we can represent with a byte?

The highest decimal value we can represent with a byte is; 255

One byte = 8 bits

Now, we also know that each bit can have the value of either 1 or 0 with the maximum value in one byte being 11111111.

Converting 11111111 to decimal is as follows;

(1 × 2^7) + (1 × 2^6) + (1 × 2^5) + (1 × 2⁴) + (1 × 2³) + (1 × 2²) + (1 × 2¹) + (1 × 2^0)

128 + 64 + 32 + 16 + 8 + 4 + 2 + 1

128 + 64 + 32 + 16 + 8 + 4 + 2 + 1 = 255

Read more on binary numbers at; link

Explanation:

One byte = 8 bits and each bit can have the value of either 1 or 0. The max value in one byte is 11111111 or 28 - 1. It is 255 in decimal value.