Engineer Shigeru Kondo teamed up with U.S. computer science student Alexander Yee to push the calculation of the mathematical constant, PhysOrg.com reported Thursday.
Pi, the ratio of a circle's circumference to its diameter, starts with 3.14159 and continues with a string of digits believed to never repeat or end.
The previous record calculation of the figure to 2.7 trillion places was made by a Fabrice Bellard, a French software engineer.
Kondo and Yee worked together while communicating by e-mail.
"Alexander provided software and I was in charge of hardware. We couldn't have achieved the results without either of us," Kondo said.
It took 90 days to calculate Pi at Kondo's home using a desktop computer with 20 external hard disks.
Kondo built the computer by himself, he said, buying parts from local electronics shops and via the Internet.
"I don't really want to say how much it cost me as my family may hear it. ... It's about $18,000," he said.