Hainan is 1.11× the size of Gulf of Finland

Hainan (province) covers about 33,800 km² (13,100 mi²) and the Gulf of Finland (gulf) about 30,400 km² (11,700 mi²). Below, both outlines are drawn at one scale and centred on each other. The Gulf of Finland outline is Natural Earth’s, checked against the published area.

33,800km²Hainan
30,400km²Gulf of Finland

100 km

Hainan
Gulf of Finland

What fits

Gulf of Finland is 90% of the size of Hainan.
Hainan is larger by 3,440 km² (1,330 mi²), which is 11% of the area of Gulf of Finland.
Measured in Belgiums: Hainan is about 1.10, Gulf of Finland about 0.99.

How they differ

Their centres are about 7,800 km apart.
On a standard web map Gulf of Finland looks larger than Hainan: Hainan at 19°N is drawn about 1.1× too large and Gulf of Finland at 60°N about 4.0×, so the map shows Gulf of Finland as 3.19× the size of Hainan, when Hainan is 1.11× the size of Gulf of Finland.
Together Hainan and Gulf of Finland cover 64,200 km², close to the size of Latvia (64,600 km², 0.5% bigger).
The gap between them, 3,440 km², is about the size of Turkish Republic of Northern Cyprus (3,320 km²).
Gulf of Finland's centre is 40.7° of latitude, about 4,530 km, farther north than Hainan's.
Hainan is a province of China; it is not drawn with its waters removed, and its measured area is the Natural Earth outline's.
The Gulf of Finland is a gulf and ranks 35th of the 42 seas on sizeversus by area.
Laid out flat, Hainan stretches about 222 km north to south and 254 km east to west; the Gulf of Finland about 177 km by 403 km.
Our measured 30,400 km² is 3.0% above Wikidata’s published figure of 29,500 km². Published areas of lakes and seas move with the water level and with what is counted, so a few percent is expected.

Who wins on what

Measure	Winner	By
Larger area	Hainan	1.11×
Farther north	Gulf of Finland	40.7° of latitude
Stretched more on a web map	Gulf of Finland	4.0× against 1.1×

Both against the same yardsticks

Yardstick	Hainan	Gulf of Finland
Belgium 30,700 km²	1.10×	0.99×
United Kingdom 244,000 km²	0.14×	0.12×
Germany 358,000 km²	0.09×	0.08×
Japan 374,000 km²	0.09×	0.08×
France 548,000 km²	0.06×	0.06×
India 3,151,000 km²	0.01×	0.01×
Brazil 8,473,000 km²	1 in 250	1 in 279
United States 9,447,000 km²	1 in 279	1 in 311
Russia 16,980,000 km²	1 in 502	1 in 559

Each figure is the place's area divided by the yardstick's.

Side by side

	Hainan	Gulf of Finland
Is a	ProvinceChina	Gulfsea on sizeversus
Area, measured	33,800 km²13,100 mi²	30,400 km²11,700 mi²
Area, published	33,900 km²Wikidata	29,500 km²Wikidata
Rank by area	–	35th of 42seas
Greatest depth	–	121 mWikidata
Latitude range	18°N to 20°N	59°N to 61°N
On the shore	–	3 on the shore

Published figures: Wikidata (CC0). A lake or a sea has no legal boundary: the measured area is that of Natural Earth’s outline, and it is shown beside the published one.

Natural Earth’s outlines of Finland, Russia and Estonia lie within 25 km of the outline of the Gulf of Finland. That is what its geometry says, and it is not a statement about who owns the water or where any border runs in it.

Similar in size to Hainan

Similar in size to Gulf of Finland

More comparisons

Sources and method

Outlines: Lakes and seas: Natural Earth 1:10m physical vectors (public domain), kept only where the measured area is within 10% of the published one. Countries and regions: Natural Earth, 1:10m Admin 0 and Admin 1, public domain.
Boundary: De facto, as drawn by Natural Earth. A lake or a sea has no legal boundary of its own; the outline is a cartographic one.
Area: Measured on the WGS84 ellipsoid from the full-detail outlines, shown rounded. The published figure comes from Wikidata (CC0), fetched 2026-11-11, and is shown beside the measured one.
Drawing: Each outline is projected with an equal-area projection centred on its own centroid, so areas stay true and the two can be laid over each other.
Data built: 2026-11-11

Full method