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FIRST CH TOOLS / Misc / 55 Timezone Converter

Time Zone Converter & World Clock

Set one date, time and zone, and every city you care about lines up side by side. See what 15:00 JST is in PST, and whether it lands on the day before or after. Check where working hours overlap, then copy a line you can paste straight into a scheduling email.

Local time in each city

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Base time
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Base UTC offset
0
Cities shown
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Working hours overlap
Working hours Early / late Night Base time 

    

      
      
      
    

  


  

    
How to Use

    
    
      
  1. Set the base momentPick the date and time you are proposing, and the zone whose clock you are reading it off. “Use current time” fills in right now; tick the box and the page becomes a world clock that updates every second.
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  2. Add the other citiesChoose the cities the other people are in. Local time, weekday, UTC offset and the difference from your base all appear, and any city that falls on a different date is marked previous day or next day.
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  3. Read the overlap and copy itThe solid cells in each bar are that city's working hours. Hours where everyone is at work are summed up in the boxes above. Once it is settled, “Copy the text” gives you a block to paste into an email. Everything runs in your browser — nothing you type is uploaded.
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About This Tool

    
Offsets come from the IANA time zone database built into your browser. Daylight saving transitions are included, so you do not have to remember that the gap to Los Angeles shrinks by an hour on the second Sunday in March. Cities are handled as zone IDs such as Asia/Tokyo and America/Los_Angeles, which also keeps PST and PDT from being mixed up.

    
“What time is 15:00 JST in PST?” converts both ways — just move the base. Set the base zone to the other side and the conversion runs in the opposite direction. The base clock sits first in the list on a tinted row, and every other city carries its difference from it, such as -16 hrs.

    
The 24-cell bar covers 00:00–23:00 of the base day. The left edge is midnight in the base zone, and how solid a cell is says whether that city is inside working hours at that moment. The orange cell marks the base time, so you can see at a glance whether nudging the meeting an hour or two puts everyone inside their working day. Working hours can be set to 9:00–18:00 and a few other common spans.

    
Wall-clock times that do not exist are moved forward. 2:30 on the second Sunday in March in the US is skipped by the clocks, so it is read as the moment after the change and flagged. Up to 12 cities can be lined up at once. Your city list is kept in your browser (localStorage) only — it is never sent to a server.

    
How this differs from the Unix timestamp converter. Epoch values such as 1755999999 out of a log belong there; lining up people's calendars belongs here. Once the slot is agreed, the ICS calendar event generator turns it into an invite.

    
You can share the setup in the URL: /en/timezone/?t=2026-09-20T15:00&tz=Asia/Tokyo&z=America/Los_Angeles,Europe/London (z is comma-separated; work takes a span such as 9-18)

  


  

    
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