Time & Time-Zone Converter – UTC, GMT, Local Maritime Time

Convert time between UTC, GMT, and local time zones with this free time conversion tool. Perfect for anyone needing quick time zone conversions – from marine operations managers coordinating global vessel schedules to port agents managing arrival times, or crew planning watch rotations across international waters.

How to Use the Time & Time-Zone Converter

1. Enter any given time and date in the input field
2. (Optional) Enter a destination port to see present time
3. View instant conversion for multiple destinations and time zones simultaneously
4. Delete or click “Clear” to do another calculation

The converter provides accurate results using standard time zone offsets and daylight saving adjustments, ensuring precision for professional maritime operations, voyage planning, and international coordination.

Common Maritime Time Zone Conversions

Universal Time Coordinated (UTC) – The Maritime Standard

UTC to Major Maritime Hubs:

• UTC to Singapore Time (SGT): UTC +8 hours
• UTC to Dubai/UAE Time (GST): UTC +4 hours
• UTC to Rotterdam/CET: UTC +1 hour (UTC +2 during CEST)
• UTC to Houston/CST: UTC -6 hours (UTC -5 during CDT)
• UTC to Panama Time (EST): UTC -5 hours
• UTC to Fujairah/UAE Time (GST): UTC +4 hours
• UTC to Hong Kong Time (HKT): UTC +8 hours
• UTC to Los Angeles/PST: UTC -8 hours (UTC -7 during PDT)

Major Shipping Hub Time Zones

Asia-Pacific Maritime Centers:

• Singapore (SGT): UTC +8, no daylight saving
• Hong Kong (HKT): UTC +8, no daylight saving
• Shanghai (CST): UTC +8, no daylight saving
• Tokyo (JST): UTC +9, no daylight saving
• Sydney (AEDT/AEST): UTC +11/+10, daylight saving October-April

Middle East & Gulf Region:

• Dubai/Fujairah (GST): UTC +4, no daylight saving
• Jeddah (AST): UTC +3, no daylight saving
• Mumbai (IST): UTC +5:30, no daylight saving

European Maritime Centers:

• Rotterdam (CET/CEST): UTC +1/+2, daylight saving March-October
• Hamburg (CET/CEST): UTC +1/+2, daylight saving March-October
• Piraeus/Athens (EET/EEST): UTC +2/+3, daylight saving March-October
• London (GMT/BST): UTC +0/+1, daylight saving March-October

Americas Maritime Centers:

• New York (EST/EDT): UTC -5/-4, daylight saving March-November
• Houston (CST/CDT): UTC -6/-5, daylight saving March-November
• Los Angeles (PST/PDT): UTC -8/-7, daylight saving March-November
• Panama (EST): UTC -5, no daylight saving
• Santos, Brazil (BRT): UTC -3, no daylight saving

Vessel Operations Time References

Watch System Conversions:

• 0000 UTC = Midnight UTC (start of nautical day)
• 0400 UTC = 04:00 UTC (morning watch)
• 0800 UTC = 08:00 UTC (forenoon watch)
• 1200 UTC = Noon UTC (afternoon watch begins)
• 1600 UTC = 16:00 UTC (first dog watch)
• 2000 UTC = 20:00 UTC (second dog watch)
• 2400 UTC = Midnight UTC (end of nautical day)

Common Operational Time Calculations:

• ETA Singapore from Rotterdam: Calculate arrival time accounting for +7 hour difference (CET to SGT)
• Port agent coordination Dubai to Houston: Manage -10 hour difference (GST to CST)
• Crew change scheduling across time zones: Account for local time at departure and arrival ports
• Bunker delivery coordination: Convert supplier local time to vessel’s operational time zone

Time & Time-Zone Conversion Formulas

UTC to Local Time Zone

Formula: Local Time = UTC + Time Zone Offset

Example: Convert 14:00 UTC to Singapore Time (SGT)

• SGT = UTC +8
• Local Time = 14:00 + 8 hours
• Local Time = 22:00 SGT

Example: Convert 18:00 UTC to Houston Time (CST, winter)

• CST = UTC -6
• Local Time = 18:00 – 6 hours
• Local Time = 12:00 CST

Local Time to UTC

Formula: UTC = Local Time – Time Zone Offset

Example: Convert 09:00 Dubai Time (GST) to UTC

• GST = UTC +4
• UTC = 09:00 – 4 hours
• UTC = 05:00 UTC

Example: Convert 15:00 Rotterdam Time (CET, winter) to UTC

• CET = UTC +1
• UTC = 15:00 – 1 hour
• UTC = 14:00 UTC

Converting Between Two Time Zones

Formula: Target Time = Source Time – Source Offset + Target Offset

Example: Convert 10:00 Singapore Time to Dubai Time

• Singapore (SGT) = UTC +8
• Dubai (GST) = UTC +4
• Difference = -8 + 4 = -4 hours
• Dubai Time = 10:00 – 4 hours
• Dubai Time = 06:00 GST

Example: Convert 16:00 New York Time (EST) to Rotterdam Time (CET)

• New York (EST) = UTC -5
• Rotterdam (CET) = UTC +1
• Difference = +5 + 1 = +6 hours
• Rotterdam Time = 16:00 + 6 hours
• Rotterdam Time = 22:00 CET

Calculating Arrival Time Across Time Zones

Formula: Arrival Time (local) = Departure Time (local) + Voyage Duration + Time Zone Difference

Example: Vessel departs Singapore at 08:00 SGT, voyage duration 72 hours to Dubai

• Departure: 08:00 SGT (UTC +8)
• Voyage duration: 72 hours (3 days)
• Time zone difference: SGT to GST = -4 hours
• Arrival calculation: 08:00 + 72 hours – 4 hours = 76:00 – 4 = 72:00
• Arrival time: 08:00 + 3 days – 4 hours = 04:00 GST (3 days later)

Example: Vessel departs Rotterdam at 14:00 CET, voyage duration 240 hours to New York

• Departure: 14:00 CET (UTC +1)
• Voyage duration: 240 hours (10 days)
• Time zone difference: CET to EST = -6 hours
• Arrival calculation: 14:00 + 240 hours – 6 hours
• Arrival time: 08:00 EST (10 days later)

Accounting for Daylight Saving Time

Formula: Adjusted Time = Standard Time ± DST Offset (typically +1 hour)

Example: Convert 12:00 UTC to Rotterdam time in summer (CEST)

• Standard offset (CET): UTC +1
• Daylight saving adjustment: +1 hour
• Total offset (CEST): UTC +2
• Rotterdam Time = 12:00 + 2 hours = 14:00 CEST

Example: Convert 20:00 UTC to New York time in summer (EDT)

• Standard offset (EST): UTC -5
• Daylight saving adjustment: +1 hour
• Total offset (EDT): UTC -4
• New York Time = 20:00 – 4 hours = 16:00 EDT

24-Hour to 12-Hour Format Conversion

Formula (for times 13:00-23:59): 12-hour time = 24-hour time – 12:00, add PM

Example: Convert 18:00 (24-hour) to 12-hour format

• 18:00 – 12:00 = 6:00
• Result: 6:00 PM

Formula (for times 00:00-11:59): Keep same number, add AM (00:00 becomes 12:00 AM)

Example: Convert 09:00 (24-hour) to 12-hour format

• Result: 9:00 AM

Understanding Time Standards and Maritime Time

Universal Time Coordinated (UTC)

Universal Time Coordinated (UTC) is the global time standard used throughout maritime operations, aviation, and international coordination. UTC is based on atomic time measurements and serves as the reference point for all time zones worldwide. Unlike local time zones, UTC does not observe daylight saving time, providing consistent reference across seasons.

In maritime operations, UTC is the standard for all official vessel logs, navigation records, radio communications, and international coordination. Ship’s clocks typically maintain UTC regardless of the vessel’s geographic position, with local time displayed separately for port operations and crew scheduling.

Maritime Applications:

• Official ship’s log entries recorded in UTC
• Navigation position reports timestamped in UTC
• Radio communications using UTC (Zulu time)
• Satellite navigation systems operating on UTC
• International distress and safety communications in UTC
• Voyage data recorder timestamps in UTC

Greenwich Mean Time (GMT)

Greenwich Mean Time (GMT) historically served as the world’s time standard, based on mean solar time at the Royal Observatory in Greenwich, London. While UTC has replaced GMT as the precise scientific standard, the terms are often used interchangeably in maritime contexts, with GMT ±0 equivalent to UTC.

The prime meridian (0° longitude) passes through Greenwich, establishing the reference point for global longitude measurements and time zones. Maritime charts and navigation systems reference this meridian for position calculations.

Ship’s Time vs. Local Time

Vessels maintain “ship’s time” for crew operations, which may differ from UTC and local port time. Ship’s time is typically adjusted gradually during ocean passages to align with destination port time zones, minimizing crew disruption from sudden time changes.

Time Zone Adjustment Practices:

• Gradual adjustment: Clocks advanced or retarded by 30-60 minutes during overnight passages
• Watch system coordination: Time changes scheduled to minimize watch rotation disruption
• Port arrival synchronization: Ship’s time aligned with local port time before arrival
• Crew rest compliance: Time adjustments managed to maintain required rest periods

Nautical Time Notation

Maritime operations use 24-hour time notation exclusively, eliminating AM/PM ambiguity critical for safety and coordination. Times are expressed as four digits (0000-2359) with optional colon separator.

Standard Maritime Time Format:

• 0000 or 00:00 = Midnight
• 0600 or 06:00 = 6:00 AM
• 1200 or 12:00 = Noon
• 1800 or 18:00 = 6:00 PM
• 2359 or 23:59 = One minute before midnight

Time Zones and Longitude

Time zones are theoretically based on 15-degree longitude increments (360° ÷ 24 hours = 15° per hour), with each zone representing one hour difference from UTC. However, political boundaries and regional preferences create irregular time zone boundaries on land.

Longitude-Based Time Calculation:

• Each 15° of longitude = 1 hour time difference
• Each 1° of longitude = 4 minutes time difference
• Eastward travel = time zones increase (UTC +)
• Westward travel = time zones decrease (UTC -)

At sea, vessels crossing time zone boundaries adjust ship’s time based on longitude change, typically making adjustments during overnight passages to minimize operational disruption.

International Date Line

The International Date Line, located approximately along the 180° meridian in the Pacific Ocean, marks where the calendar date changes. Crossing the date line westbound advances the date by one day; crossing eastbound sets the date back one day.

Maritime Date Line Considerations:

• Pacific Ocean crossings require date adjustment
• Voyage planning accounts for “lost” or “gained” days
• Crew contracts and rest period calculations adjusted for date changes
• Port arrival dates calculated accounting for date line crossings

Daylight Saving Time (DST) Impact

Daylight Saving Time adjustments affect port operations and coordination with shore-based services in regions observing DST. Maritime operations must account for these seasonal time changes when scheduling port calls, coordinating bunker deliveries, and managing crew changes.

DST Coordination Challenges:

• Northern and Southern Hemisphere DST periods differ
• Not all countries observe DST
• DST start/end dates vary by region
• Port agent coordination requires awareness of local DST status
• Bunker delivery scheduling must confirm local time including DST

Vessels operating internationally must maintain awareness of DST status at departure ports, destination ports, and intermediate stops to ensure accurate arrival time predictions and service coordination.

Frequently Asked Questions

Why do ships use UTC instead of local time?

Ships use UTC as the standard for all official records, navigation, and international communications because it provides a consistent, unchanging time reference regardless of the vessel’s geographic position or time zone. UTC eliminates confusion from time zone changes during voyages, ensures accurate coordination between vessels in different locations, and maintains standardized records for regulatory compliance. Ship’s logs, navigation position reports, radio communications, and safety systems all operate on UTC, while local time may be displayed separately for crew convenience and port operations.

How do I calculate arrival time when crossing multiple time zones?

Calculate arrival time by adding voyage duration to departure time, then adjusting for the time zone difference between departure and arrival ports. For example, if departing Singapore (UTC +8) at 10:00 local time for a 96-hour voyage to Dubai (UTC +4), calculate: 10:00 + 96 hours = 10:00 four days later, then subtract 4 hours for the time zone difference = 06:00 Dubai time. Always verify whether daylight saving time is in effect at the destination port, as this adds an additional hour adjustment during DST periods.

What’s the difference between UTC and GMT?

UTC (Universal Time Coordinated) and GMT (Greenwich Mean Time) are effectively equivalent for maritime purposes, both representing the time at 0° longitude with no daylight saving adjustment. UTC is the modern atomic-time-based standard maintained by international agreement, while GMT is the historical solar-time-based standard. Maritime operations, aviation, and scientific applications use UTC as the official standard, though “GMT” and “Zulu time” remain common informal references to the same time standard in maritime communications.

How do vessels adjust ship’s time during ocean passages?

Vessels adjust ship’s time gradually during ocean passages to align with destination port time zones while minimizing crew disruption. Typically, clocks are advanced or retarded by 30-60 minutes during overnight periods when crossing time zone boundaries. These adjustments are coordinated with watch schedules to maintain required crew rest periods and avoid sudden disruptions to sleep cycles. On long voyages crossing multiple time zones, adjustments are spread across several days rather than made all at once.

Do all countries observe daylight saving time?

No, daylight saving time is not universally observed. Many countries near the equator do not use DST because seasonal daylight variation is minimal. Major maritime hubs like Singapore, Dubai, Hong Kong, and Panama operate on standard time year-round. European and North American ports typically observe DST from March/April to October/November, though specific dates vary by region. When coordinating port operations, bunker deliveries, or crew changes, always verify the local DST status at the specific port and date to ensure accurate time coordination.

How do I convert between 24-hour and 12-hour time formats?

For 24-hour times from 13:00 to 23:59, subtract 12 and add PM (example: 18:00 – 12 = 6:00 PM). For times from 01:00 to 11:59, keep the same number and add AM (example: 09:00 = 9:00 AM). Midnight is 00:00 in 24-hour format or 12:00 AM in 12-hour format. Noon is 12:00 in both formats (12:00 PM in 12-hour). Maritime operations use 24-hour format exclusively to eliminate AM/PM confusion, which is critical for safety communications and operational coordination.

What time zone should I use for bunker delivery coordination?

Bunker delivery coordination should use the local time zone of the port where delivery will occur, clearly confirmed with the supplier to avoid confusion. When communicating delivery times internationally, specify both the local time and UTC equivalent (example: “14:00 local Dubai time, 10:00 UTC”). This dual-time specification eliminates ambiguity, especially when coordinating with suppliers in different time zones or when vessel operations staff are located remotely. Always confirm whether daylight saving time is in effect at the delivery port on the scheduled date.

How does the International Date Line affect voyage planning?

The International Date Line, located near the 180° meridian in the Pacific Ocean, requires adding or subtracting one calendar day when crossing. Vessels crossing westbound (toward Asia) advance the date by one day, while vessels crossing eastbound (toward the Americas) set the date back one day. This affects voyage duration calculations, crew contract dates, rest period tracking, and arrival date predictions. When planning Pacific crossings, account for the “lost” or “gained” day in your ETA calculations and ensure crew understand the date adjustment for personal planning.

What’s the standard time format for maritime communications?

Maritime communications use 24-hour time format with four digits and no colon, followed by the time zone designation. Standard format is “HHMM” plus zone (example: “1430 UTC” or “0800 local”). For international coordination, UTC is preferred and may be designated as “UTC,” “Z” (Zulu), or “GMT.” When using local time, always specify the time zone clearly (example: “1600 SGT” for Singapore Time). Radio communications and official logs use this standardized format to eliminate ambiguity and ensure clear understanding across language barriers and international operations.

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Gulf-Bunkering provides marine fuel trading solutions worldwide, connecting vessel operators with compliant fuel products through our knowledge of global supply networks, regional logistics, and port coordination. Accurate time zone coordination ensures efficient bunker delivery scheduling and operational planning across international waters. For marine fuel trading services, contact us at contact@gulf-bunkering.com