BIP 100: What votes are possible? I understand that, with BIP 100 as suggested by Jeff Garzik, in the first step the maximum block size can be increased from (then, after the hard fork) 2 MByte to at most double of that, so 4 MByte - without a hard fork. Depending on the miner's votes (counted for 12.000 blocks, 75% majority necessary) the block size may be increased further.

How can I, as a user start the voting process? What if I'm a miner? How do I determine the new maximum block size? Can two votes for 3 MByte and 4 MByte run in parallel?
Gregory Maxwell in IRC:


  the scheme would have the pariticiants specify the size they want, and
  at the end the period the smallest 25% would be tossed and the
  smallest remaining would be used.


So in each block there would be a field, initially set to 2 MByte. A miner is free to set any value (up to 2x the current limit).
Assuming we have the following values set in the last 12,000 blocks:


20% 2 MByte
20% 3 MByte
60% 4 MByte


Then, because only 60% want 4 MByte but 80% agree to have 3 MByte, the limit is increased to 3 MByte.

There would be a new vote every 12,000 blocks, and a decrease also would be possible if that is what the miners want.