The sharpest time zone borders on Earth
Mengmao, China and Mu-se, Myanmar are 4 km apart, close enough to share a bus route, and their clocks differ by 1 hour 30 minutes. That works out at 406.1 hours of clock difference for every thousand kilometres of ground.
Computed at 5 November 2026 at 14:04 UTC. Offsets are read at this instant, and this ranking moves more than any other on the site: several of these borders open and close by an hour as one side or the other starts or ends summer time.
The sixteen sharpest clock borders we can find
How a border's sharpness was measured
For every pair of time zones that has cities in our catalogue, we found the two cities, one from each zone, that come closest together on the ground, and we asked what those two zones read on the clock at this instant. The ranking is the clock difference divided by that distance, expressed as hours per thousand kilometres. It is a measure of how abruptly time changes when you cross a particular line, which is not the same as how big the change is.
Doing it zone by zone rather than city by city is what makes the sweep tractable: the 35,245 zone pairs are worked out once from a single pass over the catalogue, and only the offsets need re-reading when the page is served. It also gives the right answer, because the closest pair of zones is by definition found by the closest pair of cities on them.
What this cannot see is the border itself. We have cities, not boundaries, so the distance in the table is city to city and not either city to the line between them. The real gap at the border is smaller, often much smaller: at the top of this table there is a bridge, and people cross it daily. Treat the distances as upper bounds on how close the two clocks actually come.
The sharpest border in the world
Mengmao, China and Mu-se, Myanmar are 4 km apart, which is close enough to walk, and their clocks differ by 1 hour 30 minutes. That is 406.1 hours of clock difference per thousand kilometres of ground, a rate no other border on Earth comes near. Two towns that share a market, a river crossing and the same weather put their working days 1 hour 30 minutes out of step with each other, every day, permanently.
Neither side changes its clocks at any point in the year, so unlike most entries further down the table this gap is the same in January as in July. It is a permanent feature of the border rather than a seasonal one. Further down, Arica, Chile and Tacna, Peru are the clearest example of a border that breathes: 51 km apart, 2 hours apart today, and an hour closer together for the other half of the year, because only one of the two countries observes summer time.
Borders inside a single country
Not every sharp border is international. Banyuwangi, Indonesia and Negara, Indonesia are both in Indonesia, 32 km apart, and 1 hour apart on the clock. A gap that large inside one country usually means the two places are following different rules for reasons that have nothing to do with the Sun and everything to do with administration.
The general pattern is that a sharp border needs two things at once: two jurisdictions that chose different offsets, and a population living right up against the line. Plenty of large clock differences exist across empty ground, where nobody experiences them. The furthest apart in time ranking covers the opposite case, the biggest clock gaps anywhere regardless of distance, and the two lists barely overlap.
Questions about this ranking
- Where does the clock change most abruptly?
- Between Mengmao, China and Mu-se, Myanmar, 4 km apart with 1 hour 30 minutes between their clocks as this page was built.
- Is the distance measured to the border?
- No, city to city. We hold coordinates, not boundaries, so the real gap at the line is smaller than the figure printed. Read the distances as upper bounds.
- Can a border get sharper during the year?
- Yes, whenever the two sides keep different daylight saving rules. The leading pair here differs by one hour for part of the year and by 1 hour 30 minutes for the rest.
- How many zone pairs were compared?
- 35,245, being every pair of zones that has at least one city in our catalogue, each reduced to the closest approach between them.