Why do our japa counters have 20 beads instead of 16?
In the Caitanya Bhagavata, there is the pastime where Lord Caitanya is invited to take prasadam in the house of brahmanas. He answered that he would take prasadam in the house of anyone who possesses a lakh (laksesvara). The brahmanas initially understood that He was speaking about one lakh of rupees (which was an astonishing sum at those times), but the Lord quickly dispelled the confusion:
"As the devotees invited the Lord (Sri Caitanya Mahaprabhu) to take His meal in their houses, the Lord took the opportunity to teach them all this topic. When invited to take a meal, the Lord smiled and said, “First you should become a laksesvara”.
“I take meals only in the house of a laksesvara.” Hearing this, the brahmanas became worried.
The brahmanas offered prayers to the Lord, “O Gosaani, what to speak of a hundred thousand, none of us possess even a thousand. If You don’t accept meals from us, then let our entire household be burnt to ashes.”
The Lord replied, “Do you know who is a laksesvara? He is someone who daily chants a hundred thousand holy names. I call that person a laksesvara. I take meals in only such a person’s house, not in the houses of others.”
Hearing this merciful statement of the Lord, the brahmanas gave up their anxiety and became joyful. “O Lord, we will chant a hundred thousand names. Please therefore take Your meals in our houses. It is our good fortune that You are teaching us in this way.” (Caitanya Bhagavata, Antya, 9.116-125)
Traditionally, devotees in our sampradaya would chant a minimum of 64 rounds daily. Srila Bhaktisiddhanta Sarasvati introduced the standard of 16 rounds for grhasthas (who would be too busy taking care of their families) and Srila Prabhupada extended this standard to all of us.
"Now that you have beads," Swamiji says the next morning, "you should chant sixty-four rounds every day." "Sixty-four rounds?" To pronounce every word of the mantra distinctly, we require five minutes to chant a round. Sixty-four rounds would take over five hours. "Impossible!" we say. "We'll never have the time." "All right," Swamiji says. "Thirty-two rounds." "Impossible," we say. "We'll never be able to do it. It's way too much." "All right," Swamiji says. "Sixteen rounds. No less." (The Hare Krishna Explosion, p. 63)
“The Krsna consciousness movement prescribes sixteen rounds daily because people in the Western countries cannot concentrate for long periods while chanting on beads. Therefore the minimum number of rounds is prescribed. However, Srila Bhaktisiddhanta Sarasvati Thakura used to say that unless one chants at least sixty-four rounds of japa (one hundred thousand names), he is considered fallen (patita). According to his calculation, practically every one of us is fallen, but because we are trying to serve the Supreme Lord with all seriousness and without duplicity, we can expect the mercy of Lord Sri Caitanya Mahaprabhu, who is famous as patita-pavana, the deliverer of the fallen.” (Nectar of Instruction, text 5)
In other words, the 16 rounds that we struggle so much to chant are not the perfection, but just the beginning, and the counters are there to remember this.
The traditional way is to tie the counter on the japa bag with 16 beads to one side and 4 to the other. The extra beads are for counting how many times we chanted 16 rounds: 16 x 4, totalizing 64 rounds. If we make the calculation, each round equates to 1728 names, 16 rounds to 27648 names and 64 rounds to 110592. However, traditionally 64 rounds are considered a lakh, or a hundred thousand names, the measure that every vaishnava was supposed to chant daily in the times of Mahaprabhu. A few senior vaishnavas (usually bajananandis) would be able to chant two lakhs, or 128 rounds, while Haridasa Thakura was able to daily chant three lakhs, or 192 rounds. Srila Bhaktisiddhanta Saraswati Thakura also chanted 3 lakhs daily for a period of approximately 9 years, when he was performing a vow of chanting a billion names. Right after concluding this vow, he started preaching, and the results are registered in the pages of history. Srila Prabhupada also used to chant many rounds when he was living in Vrindavana, as part of his preparation for coming to preach in the west.