To convert from decimal to binary, subtract off powers of 2, and if the result is positive, write a 1. Otherwise write a 0. This method assumes that the highest power of 2 needed for this conversion is already known. Making a reasonable guess isn't hard if the powers of 2 are consulted. An alternate way, a straightforward algorithm, is to start with the 0th power of 2, 1, and subtract it. If the result is positive, guess higher. Continue this until a negative number is obtained, then back off to the previous power of 2.

Here is a table of some of the powers of 2:

               n                         n                           n
     n        2            n            2          n                2
   ------------------------------------------------------------------
     0        1           11          2048         22       4,194,304
     1        2           12          4096         23       8,388,608
     2        4           13          8192         24      16,777,216
     3        8           14        16,384         25      33,554,432
     4       16           15        32,768         26      67,108,864
     5       32           16        65,536         27     134,217,728
     6       64           17       131,072         28     268,435,456
     7      128           18       262,144         29     536,870,912
     8      256           19       524,288         30   1,073,741,824
     9      512           20     1,048,576         31   2,147,483,648
    10     1024           21     2,097,152         32   4,294,967,296