How accurate is the longitude/15 formula?

It is accurate for oceanic and remote regions but can be off by 30 minutes to 1.5 hours near political borders. Countries like India (UTC+5:30), Iran (UTC+3:30), and China (single UTC+8 across 5 geographic zones) are well-known exceptions.

What is the difference between meridian time and civil time zones?

Meridian time divides Earth into uniform 15-degree solar longitudinal slices. Civil time zones (IANA) are political designations with customized borders, DST variations, and fractional offsets.

Why is latitude requested if only longitude determines the offset?

Latitude completes the geographic coordinate pair to specify an exact physical location on Earth, even though solar meridian time zones depend solely on longitude.

Does this account for Daylight Saving Time?

No. The formula is purely geographic. During Daylight Saving Time, clocks in many regions advance one hour beyond the standard meridian offset. Always check a live time zone database (such as IANA tz data) if legal local time matters.

What coordinate format should I use?

Use decimal degrees. Latitude ranges from −90 (South Pole) to 90 (North Pole). Longitude ranges from −180 (International Date Line west side) to 180 (International Date Line east side). West longitudes are negative.

Timezone From Coordinates

Enter geographic coordinates to calculate the theoretical meridian time zone and solar UTC offset (lon / 15), distinct from civil political time zones.

Enter Coordinates

Latitude (decimal degrees, −90 to 90)

Longitude (decimal degrees, −180 to 180)

Try an example

Enter coordinates and click "Estimate Timezone" to see the UTC offset.

Summary

Enter geographic coordinates to calculate the theoretical meridian time zone and solar UTC offset (lon / 15), distinct from civil political time zones.

How it works

Enter decimal coordinates: latitude (−90 to 90) specifies position, while longitude (−180 to 180) sets the meridian.
The tool divides the longitude by 15 and rounds to the nearest integer to get the theoretical meridian UTC offset.
The estimated offset is displayed along with the probable UTC label (e.g. UTC+5 or UTC−3).
A breakdown shows the raw calculation so you can understand the approximation.
A disclaimer highlights that legal civil time zones differ due to political borders, Daylight Saving Time, or fractional offsets.

Use cases

Quickly estimate a time zone when only GPS coordinates are available.
Cross-check coordinate data against expected time zones in GIS workflows.
Teach or demonstrate how the 24-meridian time zone system works.
Estimate UTC offset for a remote location before more precise lookup is possible.
Pre-flight checks for drone or field operations where network access is limited.
Validate exported coordinate records that include a UTC offset field.

Frequently Asked Questions

Last updated: 2026-09-22 · Reviewed by Nham Vu