# The Urinal Problem — Five urinals, nine people

> Five urinals, nine people (iPhone/iPad app by syoutarou ookura.)

- Source: https://appshunter.io/ios/app/the-urinal-problem/id6805428175 (this page in markdown: same URL + `.md`)
- Developer: [syoutarou ookura](https://appshunter.io/developer/1614144503)
- Category: Entertainment, Education
- Price: Free
- Age rating: 9+
- Requires: iOS 15.0 · 18 MB
- Languages: American English
- Released: 2026-09-09
- Data updated: 2026-10-02
- User reviews in markdown: https://appshunter.io/ios/app/the-urinal-problem/id6805428175/reviews.md

## What is The Urinal Problem?

The unwritten rule of the men's room, checked against the numbers.

Pick the urinal that is furthest from everyone else. Nobody taught it to you, yet everybody follows it. So what actually happens when nine people walk into a row of five urinals?

WHAT YOU THINK YOU KNOW, MEASURED
Call a spot comfortable when the nearest occupied urinal is at least two away. The ceiling for n urinals is then ceil(n/2) people — three out of five, a 60% occupancy rate. The fourth arrival always ends up next to somebody.

THE FIRST PERSON DECIDES EVERYTHING
If the first arrival takes an odd-numbered urinal (1, 3 or 5), three people can stay comfortable. If they take an even one (2 or 4), the ceiling drops to two — before anyone else has even walked in. One opening move fixes the throughput for everyone who follows.

The rule of thumb: take an odd-numbered urinal first.

WHAT YOU CAN DO
- Simulate 2 to 12 urinals and 1 to 30 people
- Watch the whole thing play out in pictograms at 1x / 2x / 4x, with a scrub bar
- See comfort rate, peak comfortable count and the theoretical maximum
- Read the timeline as a Gantt chart; cramped stretches are hatched
- See why each person chose their spot — far-end seekers, wall huggers, germaphobes and people who ignore the rule entirely
- Export the result as a vertical card image and share it
- Every run is fully reproducible from its seed, and kept in your history
- A short explainer page covers the theory

NOTES
- Everyone is drawn as a pictogram, the way restroom signage does it
- Completely free. No ads, no in-app purchases
- No network access and no permissions. Everything runs on your device
- English and Japanese


## Version history (last 3 releases)

### 1.1.1 — 2026-09-29

App Storeにアプリの使い方がわかるプレビュー動画を追加しました。

### 1.1.0 — 2026-09-18

Export your simulation as an MP4 video. Choose 9:16 vertical or 1:1 square, and 15 or 30 seconds. Videos are created entirely on your device and can be shared right away. You can also make a video from any run in History. Fixed a bug that saved duplicate history entries.

### 1.0 — 2026-09-02

No release notes.

## More apps by syoutarou ookura

- [BINGO Online](https://appshunter.io/ios/app/bingo-online/id1614144501)
- [【メモ機能付き】クレーン・デリック運転士試験対策一問一答形式](https://appshunter.io/ios/app/id1664065788)
- [【メモ機能付き】衛生工学衛生管理者試験対策一問一答形式](https://appshunter.io/ios/app/id1664434037)
- [【メモ機能付き】あん摩マッサージ指圧師試験対策一問一答形式](https://appshunter.io/ios/app/id1665067407)
- [【メモ機能付き】知的財産管理技術検定試験対策一問一答形式](https://appshunter.io/ios/app/id1665068478)
- [【メモ機能付き】丙種危険物取扱者試験対策 一問一答形式](https://appshunter.io/ios/app/id6443748279)

All apps by syoutarou ookura: https://appshunter.io/developer/1614144503

---

*Data collected daily from the US App Store and indexed by [AppsHunter](https://appshunter.io/). User reviews are verbatim App Store reviews. Ratings, prices and chart positions refresh continuously; this snapshot is from 2026-10-02.*