Knowledge of World Time Difference

iPhone App, compare time difference cities in the world.

Price: Free


  • [Jan. 23, 2018] v1.0.0 available at App Store

About this app

Because the Earth is a sphere, cities around the world uses different clocks. When London is at 9 a.m., New York is at 4 am and Tokyo is at 6pm. It's called timezone.

With the "World Clock" in iOS preinstalled application "Clock", you can know the current time of any place in the world. But if you want to know the time of another place at 9 p.m. in this place, the calculation is not easy. When is noon at a place, what time is it in another place?

With this application you can easily compare the times in places you specified around the world with each other.


Attention to the following when using this application.

  • Please turn off "Rotation Lock" when using this application.
  • UTC is abbreviation of Coordinated Universal Time. It's considered interchangeable with GMT(Greenwich Mean Time). In this app, we use UTC instead of GMT.
  • Althogh conversion from city name to time zone is done inside the application, this app uses iOS standard feature to calculate the time difference and the daylight saving time for its time zone. If there is an error on the iOS, it is displayed as it is.
  • [Known Issue]From 8 Jan, 2018 time zone of "Sao Tome and Principe" [Africa/Sao_Tome] has been changed from UTC to WAT (UTC - 1), but not supported in iOS 11.2.2.

Runtime Environment

  • iOS9, iOS10, iOS11
  • Where the above OS is running on iPhone, iPod touch.
  • English, Japanese.
  • Portrait, Landscape. Please turn off "Rotation Lock" before using this application.

Version History

First release.

Support & Credit


In developing this app, it was helped by a number of open source projects and free software and free material. We also use widely published research results and other articles. Thank you for the people who is related to that.