According to the 15 February 1890 The Electrical World volume XV, page 106
One queer notion he had was to work out everything by three or the powers of three. He would also calculate the cubes of every article of food put on the table at meals
However, in the 1892 book Experiments with Alternate Currents of High Potential and High Frequency, written by Tesla himself, the entire biographical article of Electrical World is reproduced as an introduction, but omitting the sentence "He would also calculate the cubes of every article of food put on the table at meals..."
According to Tesla, A Man Out Of Time:
Promptly at eight o’clock a patrician figure in his thirties was shown to
his regular table in the Palm Room of the Waldorf-Astoria Hotel. Tall
and slender, elegantly attired, he was the cynosure of all eyes, though
most diners, mindful of the celebrated inventor’s need for privacy,
pretended not to stare.
Eighteen clean linen napkins were stacked as usual at his
place. Nikola Tesla could no more have said why he favored numbers
divisible by three than why he had a morbid fear of germs or, for that
matter, why he was beset by any of the multitude of other strange
obsessions that plagued his life.
Abstractedly he began to polish the already sparkling silver
and crystal, taking up and discarding one square of linen after another
until a small starched mountain had risen on the serving table. Then,
as each dish arrived, he compulsively calculated its cubic contents
before lifting a bite to his lips. Otherwise there could be no joy in
The editor went his way and Tesla returned his attention to the
cubic contents of his dessert course. He had barely completed his
calculations when a messenger appeared at his table and handed him
In the house caused him acute discomfort. In research, if he dropped
little squares of paper in a dish filled with liquid, it caused a peculiar
and awful taste in his mouth. He counted steps when walking,
calculated the cubic contents of soup plates, coffee cups, and pieces of
food. If he failed to do so his meal was unenjoyable — hence his
preference for dining alone.
Also, according to the November 1901 The Junior Munsey:
Whatever meets his eye, a house, a ship, a cloud, a mountain, impels him to a mental calculation of its cubic contents