Three spells at the top
The ranking list gives dates for each period rather than a single achievement. It records 15,151 digits from 4 June to 11 July 1979; 20,000 digits from 2 October 1979 to 26 June 1980; and 40,000 digits from 10 March 1987 to 17 February 1995.
Read together, those lines describe a competitive era rather than one attempt. The first record lasted five weeks before it fell. The second lasted under nine months. The third lasted nearly eight years, which in a discipline that was expanding rapidly is an unusually long reign.
What 40,000 digits means
Forty thousand decimal places is a sequence with no pattern to exploit. Pi's digits behave, for the purposes of memory, as if they were random, so nothing can be reconstructed and every place must be held individually or as part of a memorised chunk.
The 1987 record also came at a point when the pi lists were being rewritten repeatedly. That it survived to 1995 says something about the size of the jump: Tomoyori had doubled the previous mark he himself had set, and it took the field the better part of a decade to answer.
Where the record went next
The modern figures dwarf it. Guinness World Records recognises Rajveer Meena of India for 70,000 digits in 9 hours 7 minutes, recited blindfolded on 21 March 2015. The Pi World Ranking List also carries Suresh Kumar Sharma's 70,030 digits in 17 hours 14 minutes, which Guinness does not.
The largest claim of all belongs to another Japanese memoriser, Akira Haraguchi, who says he recited 111,700 digits in 16 hours 30 minutes in 2006 and has never been formally recognised by Guinness. Tomoyori's 40,000 sits in the history of the discipline rather than at the top of its current table.
How the record is kept
There is no single authority for pi recitation. The Pi World Ranking List maintains the historical register and the current standings; Guinness World Records runs a separate and stricter process. Because the two differ on verification, they differ on who holds what.
A figure quoted without its register is therefore close to meaningless, which is why the dates and the source are given explicitly on this page. Tomoyori's three periods come from the ranking list's own detail page for him.
What is documented, and what is not
Documented by the Pi World Ranking List: the three record-holding periods and their exact opening and closing dates, and his identification as a world record holder from Japan.
Not documented in the pages used here: his age or date of birth, which is why this page carries no birth year; his occupation; how long each recitation took; where the attempts were made; and how he prepared. The ranking list refers to an interview with him elsewhere on its site, which was not consulted for this page, and nothing beyond the record table is claimed here.
| 인물 | 국가 | 이정표 | 나이 / 기록 |
|---|---|---|---|
| Hideaki Tomoyori | 일본 | 원주율 암기 세계 기록 3회 보유 | — |
| Rebecca Sharrock | 호주 | 자전적 기억력(HSAM) | — |
| Marc Umile | 미국 | 원주율 15,314자리 암송 | — |
| Krishan Chahal | 인도 | 원주율 43,000자리 암송 | — |
| Rick de Jong | 네덜란드 | 원주율 22,612자리 암송 | — |
What is documented — and what is not
✓ Documented
- Listed by the Pi World Ranking List as a world record holder
- Held the record at 15,151 digits from 4 June to 11 July 1979
- Held it at 20,000 digits from 2 October 1979 to 26 June 1980
- Held it at 40,000 digits from 10 March 1987 to 17 February 1995
? Unverified, disputed or wrong
- No age, date of birth or occupation in these sources
- The durations and venues of the attempts are not given
- An interview with him exists on the ranking list's site but was not consulted for this page
Questions people ask about Hideaki Tomoyori
What is Hideaki Tomoyori known for?
Holding the pi memorisation world record three times, most notably at 40,000 digits from 10 March 1987 until 17 February 1995.
How many digits did he memorise?
The Pi World Ranking List records 15,151, then 20,000, then 40,000.
How long did his last record stand?
From 10 March 1987 to 17 February 1995, nearly eight years.
How old is Hideaki Tomoyori?
No age or date of birth appears in the pages used here.
Who holds the record now?
Guinness World Records recognises Rajveer Meena for 70,000 digits; the Pi World Ranking List also carries Suresh Kumar Sharma's 70,030.
How long did his recitations take?
The pages used here give the dates of the records but not the durations of the attempts.
Is Hideaki Tomoyori on Wikipedia?
The research file for this page treats it as uncertain and no article is cited here.
Where is Hideaki Tomoyori now?
Nothing after 1995 appears in the sources used here.
Quick quiz: how well do you know Tomoyori’s story?
How many digits did Hideaki Tomoyori reach in 1987?
Until when did that record stand?
How many times does the ranking list record him as world record holder?
Sources
- Hideaki Tomoyori - details — Pi World Ranking List
- Pi World Ranking List - Pi — Pi World Ranking List
- Pi Day 2017: Meet the record-holders for memorizing digits of pi — Mic, 2017-03-14
Checked by the Geniuses.club editorial team. Ages are given as of September 2026.
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