Similarly to how the digits in decimal represent values of increasing powers of 10 (the far right digit is the number of units, the next digit to the right is the number of 10s, the next digit along is the number of 10^{2}s, etc.), the digits in binary represent powers of 2 (the far right digit is units, next along is 2s, next along is 2^{2}s, etc.). Therefore to calculate this binary number into decimal we must add the values represented by each digit. The far left digit is the 1s and in our example contains a 1 so we add one 1 to our sum. The next digit to the right is the 2s and contains a 1 in out example so we add one 2 to our sum. The next digit is the 4s and contains a 0 so we do not add any 4s to our sum. Similarly, we add one 8 and one 16 for the next digits. This makes our sum 1 + 2 + 8 + 16 = 27 so the value of 11011 in decimal is 27.