code: def calculate_raw_tx_size(num_inputs, num_outputs):
      
      tx_size = (num_inputs * BYTES_PER_INPUT) + (num_outputs *
                                                  BYTES_PER_OUTPUT) + FIXED_EXTRA_BYTES + num_inputs
      return tx_size
docs: To calculate the transaction size:
          tx_size = (num_inputs * BYTES_PER_INPUT) + (num_outputs * BYTES_PER_OUTPUT) + FIXED_EXTRA_BYTES +/- num_inputs
  
      We'll choose the upper bound, so:
          +/- num_inputs  =>  + num_inputs
  
      Equation and constants are taken from http://bitcoin.stackexchange.com/a/3011.
  
      :param num_inputs:
      :param num_outputs:
      :return: