Time Zone from Longitude Calculator
Estimate the nominal UTC offset and local solar time for any longitude, based on 15° of longitude per hour.
How it works
exact offset (h) = longitude / 15 · nominal zone = round(longitude / 15)
The Earth turns 360° in 24 hours, so every 15° of longitude corresponds to one hour of solar time. This gives the theoretical time zone from longitude alone. Real political time zones follow country and state borders and daylight saving, so they often differ from this ideal by an hour or more.
Worked example
Longitude −74.006°: exact offset = −74.006 / 15 = −4.934 h. Rounded, that is UTC−5 — which matches US Eastern Standard Time, about 4 minutes of solar time from the zone centre at −75°.
Sources: Time zone — Wikipedia
Frequently asked questions
Why does this differ from the real time zone?
Legal time zones are drawn along borders for convenience and may apply daylight saving, so places share a clock time even when their solar times differ. Some regions also use half-hour or 45-minute offsets.
What is solar time?
Solar time is set by the Sun’s position, reaching noon when the Sun is highest. Longitude/15 gives each location’s mean solar offset from UTC.
Do any places use non-integer offsets?
Yes — India is UTC+5:30 and Nepal UTC+5:45, for example. This model returns the nearest whole hour.
Related calculators
Educational estimate. Uses a spherical-Earth model; results differ slightly from ellipsoidal (WGS84) calculations.