Time Zone Converter: How to Convert Between World Time Zones
Whether you are scheduling a meeting with colleagues in Tokyo, calling family in London, or booking a flight from New York to Sydney, understanding time zones is essential. This guide explains how time zones work, how to convert between them, and what to watch out for — especially during daylight saving time changes.
What Are Time Zones?
The Earth is divided into 24 standard time zones, each roughly 15 degrees of longitude wide (360 degrees / 24 hours = 15 degrees per hour). As the Earth rotates, the sun appears to move across the sky, and each zone sets its clocks to a different hour.
The reference point is UTC (Coordinated Universal Time), which runs through the Royal Observatory in Greenwich, London. Time zones are expressed as offsets from UTC, such as UTC-5 (Eastern Standard Time) or UTC+9 (Japan Standard Time).
Common Time Zone Offsets
| Time Zone | UTC Offset | Major Cities |
|---|---|---|
| UTC | UTC+0 | London (winter), Reykjavik |
| EST (Eastern) | UTC-5 | New York, Toronto |
| CST (Central) | UTC-6 | Chicago, Mexico City |
| PST (Pacific) | UTC-8 | Los Angeles, Vancouver |
| CET (Central Europe) | UTC+1 | Paris, Berlin, Rome |
| IST (India) | UTC+5:30 | Mumbai, New Delhi |
| CST (China) | UTC+8 | Beijing, Shanghai |
| JST (Japan) | UTC+9 | Tokyo, Seoul |
| AEST (Australia East) | UTC+10 | Sydney, Melbourne |
How to Convert Between Time Zones
Converting time between zones follows a simple formula:
- Find the UTC offset for both time zones
- Calculate the difference: Target offset - Source offset
- Add the difference to your source time
- Adjust for day change if the result goes past 24:00 or before 00:00
Example: What time is 3:00 PM EST in Tokyo?
EST = UTC-5, JST = UTC+9
Difference = 9 - (-5) = 14 hours
3:00 PM + 14 hours = 3:00 AM next day
Result: 3:00 AM JST (next day)
Example: What time is 9:00 AM PST in London?
PST = UTC-8, GMT = UTC+0
Difference = 0 - (-8) = 8 hours
9:00 AM + 8 hours = 5:00 PM
Result: 5:00 PM GMT (same day)
Daylight Saving Time (DST)
Many countries shift their clocks forward by 1 hour during summer months. This is called Daylight Saving Time and it changes the effective UTC offset:
- EST (UTC-5) becomes EDT (UTC-4) during summer
- PST (UTC-8) becomes PDT (UTC-7) during summer
- CET (UTC+1) becomes CEST (UTC+2) during summer
- GMT (UTC+0) becomes BST (UTC+1) during summer
Important: DST start and end dates vary by country. The US changes on different dates than the EU, and many countries (Japan, China, most of Africa) do not observe DST at all. Always verify whether DST is in effect during your target date.
Half-Hour and 45-Minute Zones
Not all time zones are whole-hour offsets. Some regions use half-hour or even 45-minute offsets:
- India (IST): UTC+5:30
- Newfoundland (NST): UTC-3:30
- Nepal (NPT): UTC+5:45
- Chatham Islands (CHAST): UTC+12:45
The International Date Line
The International Date Line runs roughly along the 180-degree meridian in the Pacific Ocean. Crossing it from west to east, you lose a day. Crossing from east to west, you gain a day.
This is why when it is Monday afternoon in Los Angeles, it is already Tuesday morning in Tokyo — the date has changed even though only a few hours of clock time separate them.
Quick Conversion Reference
| When it's 12:00 PM (Noon) UTC | Local Time |
|---|---|
| New York (EST) | 7:00 AM |
| Los Angeles (PST) | 4:00 AM |
| London (GMT) | 12:00 PM |
| Paris (CET) | 1:00 PM |
| Mumbai (IST) | 5:30 PM |
| Beijing (CST) | 8:00 PM |
| Tokyo (JST) | 9:00 PM |
| Sydney (AEST) | 10:00 PM |
Tips for Scheduling Across Time Zones
- Use UTC as your reference: Convert both zones to UTC first, then compare
- Check DST dates: The US and EU change clocks on different dates
- Watch for date changes: A meeting at 10 PM EST may be the next day in Asia
- Use a time zone converter for complex multi-zone scheduling
Key Takeaways
- Time zones are offsets from UTC (Coordinated Universal Time)
- Conversion: find both UTC offsets, calculate the difference, add to source time
- Daylight saving time changes UTC offsets by +1 hour in many regions
- Some zones use half-hour or 45-minute offsets (India, Nepal, Newfoundland)
- The International Date Line causes the calendar date to change
- Use our Time Zone Converter for instant conversions across 17 world time zones