Under the 1982 United Nations Convention on the Law of the Sea (UNCLOS), a country’s territorial waters extend up to 12 nautical miles from its coastal baseline. That works out to roughly 13.8 land miles, or about 22.2 kilometers. The 12-mile limit is the standard now followed by the vast majority of coastal nations and by the 170 states plus the European Union bound to UNCLOS as of January 2026.1United Nations. United Nations Convention on the Law of the Sea – Part II
Before UNCLOS settled the question, national claims varied wildly. Some countries claimed as little as three miles from shore; others claimed hundreds. The convention replaced that patchwork with a single ceiling, which is why the 12-mile figure now appears in almost every dispute over fishing, navigation, and coastal enforcement.
Where the 12 Miles Are Measured From
The distance is not measured from the beach you can see. It runs outward from a legally defined line called the baseline. The default is the normal baseline, which follows the coast’s low-water mark as shown on official nautical charts.
Where a coastline is deeply indented or fringed with islands, a country may instead draw straight baselines connecting the outermost coastal points.2UNTERM. Straight Baseline Water on the landward side of those straight lines becomes internal waters, where the state’s authority is absolute and there is no right of foreign passage at all. The 12-mile territorial sea then begins on the seaward side of that line, which can push the outer edge of territorial waters much farther from the physical shore than a casual look at a map would suggest.
A third method applies to archipelagic states such as Indonesia and the Philippines. They may draw baselines connecting the outermost islands of the archipelago, provided the enclosed water-to-land ratio falls between 1-to-1 and 9-to-1 and no single segment exceeds 100 nautical miles, with a narrow exception allowing up to three percent of segments to reach 125 nautical miles.3United Nations. United Nations Convention on the Law of the Sea – Part IV The territorial sea is then measured outward from those island-to-island baselines rather than from each island’s own low-water mark.
What a Country Controls Inside Its Territorial Waters
Within the 12-mile limit, a coastal state exercises sovereignty over the water, the seabed, the subsoil beneath it, and the airspace above.1United Nations. United Nations Convention on the Law of the Sea – Part II Domestic law on customs, immigration, pollution, and criminal conduct all apply. The state can designate shipping lanes, impose environmental rules, and prosecute crimes committed in those waters.
For most practical purposes, the territorial sea is an extension of national territory. It is simply wet. That is the reason the 12-mile line matters so much: it marks where a country’s ordinary lawmaking power reaches, and where foreign vessels are treated as being inside another state’s jurisdiction.
Innocent Passage: The One Big Limit
Sovereignty inside the 12-mile zone is not total. Foreign ships have a right of innocent passage. They may transit another country’s territorial sea without asking permission, so long as the passage is continuous, reasonably direct, and not threatening to the coastal state.1United Nations. United Nations Convention on the Law of the Sea – Part II A ship can stop only for reasons tied to ordinary navigation, such as anchoring in distress or rescuing someone in danger.
Certain conduct destroys the innocent character of the transit and lets the coastal state step in. Weapons practice, intelligence collection, launching or recovering aircraft, fishing, deliberate pollution, and unauthorized scientific research all cross the line.4United States Department of State. United States Responses to Excessive National Maritime Claims Submarines using innocent passage must travel on the surface and fly their flag. A coastal state may temporarily suspend innocent passage in a specific area for security reasons, for example during a naval exercise, but it cannot close its territorial sea to foreign shipping on a permanent basis.
A different and more permissive rule, called transit passage, applies in narrow straits used for international navigation, such as the Strait of Hormuz or the Strait of Malacca. There, ships and aircraft of all nations pass freely, submarines are not required to surface, and the bordering states cannot suspend passage.5United Nations. United Nations Convention on the Law of the Sea – Part III
What Lies Beyond the 12-Mile Line
It is easy to assume that everything a country regulates offshore counts as territorial waters. It does not. UNCLOS creates separate zones beyond the 12-mile limit where a coastal state has real but narrower authority, and neither zone is the same as territorial waters.
From 12 to 24 nautical miles offshore lies the contiguous zone. Inside it, a coastal state can act only to prevent or punish violations of its customs, tax, immigration, and health laws.1United Nations. United Nations Convention on the Law of the Sea – Part II It is an enforcement buffer, not sovereign territory.
Farther out, the exclusive economic zone (EEZ) reaches up to 200 nautical miles from the baseline. There the coastal state controls exploration and use of natural resources such as fish, oil, gas, and offshore energy, and can license drilling, set fishing quotas, and create marine conservation areas.6United Nations. Convention on the Law of the Sea – Part V Exclusive Economic Zone But the EEZ is not territory. Foreign ships and aircraft keep full freedom of navigation and overflight, other countries may lay submarine cables and pipelines, and the coastal state has no general authority to restrict passage or apply its domestic law the way it does inside 12 miles.
How the United States Handles the 12-Mile Rule
The United States has never ratified UNCLOS. The treaty stalled in the Senate over the deep-seabed mining provisions in Part XI, and as of early 2026 the U.S. remains a non-party even though every administration since Reagan has supported eventual ratification.7U.S. Congress. Implementing Agreements Under the United Nations Convention on the Law of the Sea
In practice, the U.S. follows the 12-mile standard anyway. The Reagan administration declared it would observe UNCLOS provisions, other than Part XI, as customary international law, and later administrations have kept that stance. The U.S. extended its own territorial sea from 3 to 12 nautical miles by presidential proclamation in 1988.8National Archives. Proclamation 5928 – Territorial Sea of the United States of America An earlier 1983 proclamation established the 200-mile U.S. EEZ.9Federal Register. Proclamation 5030 of March 10, 1983: Exclusive Economic Zone of the United States of America
Enforcement inside those U.S. waters falls primarily to the Coast Guard, which has broad statutory authority to board vessels, conduct searches, make arrests, and seize ships for violations of federal law both in waters under U.S. jurisdiction and, for certain offenses, on the high seas.10Office of the Law Revision Counsel. 14 USC 522: Law Enforcement So while the U.S. is not formally bound by UNCLOS, the 12-mile territorial sea, the 24-mile contiguous zone, and the 200-mile EEZ are all part of how the country actually draws its offshore authority.