I was very
proud when I figured out how to do this.
This method starts from the left and only requires you to remember one number (instead of remembering the powers of two like some methods require). You may find it complicated to convert higher numbers, if you discover you aren't good at multiplying by two in your head. (If so, learn the powers of two and try another method mentioned in this node.)
(1) start at the left and move right
(2) put the number zero in your head
(3) for each digit, add the digit to the number in your head and then multiply the answer by two unless you're at the last digit.
Like So: 110001
Start with 0.
Add 1 = 1.
Multiply by 2 = 2.
Add 1 = 3.
Multiply by 2 = 6.
(6 + 0) * 2 = 12
(12 + 0) * 2 = 48
48 + 1 = 49
The beauty is, this works with converting any base to base 10. Simply multiply by that base instead of by 2.