The territorial sea of Tonga comprises those areas of the sea having, as their inner limits, the baseline described in sections 5 and 6 of this Act and, as their outer limits, a line measured seaward from that baseline, every point of which line is distant 12 nautical miles from the nearest point of the baseline.
Baseline of territorial sea
- (1) Except as otherwise provided in section 6 of this Act, the baseline from which the breadth of the
territorial sea of Tonga is measured shall be:
(a) In the case of islands situated on atolls or of islands having fringing reefs, the low-water mark along the
seaward edge of the reef;
(b) In the case of islands not situated on atolls or of islands not having fringing reefs, the low-water mark
along the coast of those islands.
(2) For the purposes of this section, a low-tide elevation that lies wholly or partly within the breadth of sea
that would be territorial sea if all low-tide elevations were disregarded for the purpose of the measurement of the
breadth of the territorial sea shall be treated as an island.
https://www.un.org/depts/los/LEGISLATIONANDTREATIES/PDFFILES/TON_1989_Act.pdf
Tonga's 12 nautical mile zone was extracted from the Global Marine Regions platform (https://www.marineregions.org/) since they have not deposited formally with UNDOALOS.
