Turning longitude into local time
Earth turns 360 degrees in the 1,440 minutes of a day, which puts one degree of longitude at exactly four minutes. Enter the longitude of your location and the longitude of the standard meridian your clocks follow, and the gap between local mean time and standard time is worked out to the second. The result also shows what the standard clock reads at local mean noon, and what local mean time reads when the standard clock strikes noon.
A standard meridian sits at the zone's UTC offset multiplied by 15 degrees, so a zone five hours behind UTC uses 75 degrees west. A spot at 87.6 degrees west therefore runs 9 minutes 36 seconds ahead of its 90 degree meridian. Pick east or west in the direction field and write the longitude as a positive number. The math uses nothing but the two longitudes, with no place names and no daylight saving list. (As of October 2026)
The moment the sun actually crosses overhead drifts back and forth through the year by up to a quarter of an hour, because of Earth's orbital shape and axial tilt. That drift is called the equation of time and it is not applied here, so every figure is mean time. Sunrise and sunset times are not covered.
Frequently asked questions
Four minutes. The 1,440 minutes of a day divided by 360 degrees, which makes 15 degrees exactly one hour.
Multiply the zone's UTC offset by 15 degrees. A zone five hours behind UTC has its meridian at 75 degrees west.
Because of the equation of time. True solar noon shifts from day to day, while this tool reports mean time without that correction.