Montana is 1.09× the size of Great Barrier Reef

Montana (state) covers about 379,000 km² (147,000 mi²) and the Great Barrier Reef (reef) about 348,000 km² (135,000 mi²). Below, both outlines are drawn at one scale and centred on each other. The Great Barrier Reef outline is Natural Earth’s, checked against the published area.

379,000km²Montana
348,000km²Great Barrier Reef

200 km

Montana
Great Barrier Reef

What fits

Great Barrier Reef is 92% of the size of Montana.
Montana is larger by 31,100 km² (12,000 mi²), which is 8.9% of the area of Great Barrier Reef.
Measured in Belgiums: Montana is about 12.4, Great Barrier Reef about 11.4.

How they differ

Their centres are about 12,400 km apart.
A standard web map misstates the comparison: Montana at 47°N is drawn about 2.2× too large and Great Barrier Reef at 18°S about 1.1×, so the map shows Montana as 2.12× the size of Great Barrier Reef instead of 1.09×.
Together Montana and Great Barrier Reef cover 728,000 km², close to the size of Chile (736,000 km², 1.2% bigger).
The gap between them, 31,100 km², is about the size of Belgium (30,700 km²).
Montana's centre is 65.2° of latitude, about 7,250 km, farther north than Great Barrier Reef's.
Montana is a state of the United States; it is not drawn with its waters removed, and its measured area is the Natural Earth outline's.
The Great Barrier Reef is a reef and ranks 17th of the 42 seas on sizeversus by area.
Laid out flat, Montana stretches about 527 km north to south and 916 km east to west; the Great Barrier Reef about 1,580 km by 1,130 km.
Wikidata’s published figure of 348,000 km² agrees with our measured 348,000 km², to within 2%.

Who wins on what

Measure	Winner	By
Larger area	Montana	1.09×
Farther north	Montana	65.2° of latitude
Stretched more on a web map	Montana	2.2× against 1.1×

Both against the same yardsticks

Yardstick	Montana	Great Barrier Reef
Belgium 30,700 km²	12.4×	11.4×
United Kingdom 244,000 km²	1.56×	1.43×
Germany 358,000 km²	1.06×	0.97×
Japan 374,000 km²	1.02×	0.93×
France 548,000 km²	0.69×	0.64×
India 3,151,000 km²	0.12×	0.11×
Brazil 8,473,000 km²	0.04×	0.04×
United States 9,447,000 km²	0.04×	0.04×
Russia 16,980,000 km²	0.02×	0.02×

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

Side by side

	Montana	Great Barrier Reef
Is a	StateUnited States	Reefsea on sizeversus
Area, measured	379,000 km²147,000 mi²	348,000 km²135,000 mi²
Area, published	381,000 km²Wikidata	348,000 km²Wikidata
Rank by area	–	17th of 42seas
Latitude range	44°N to 49°N	24°S to 10°S
On the shore	–	1 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 Australia lie within 25 km of the outline of the Great Barrier Reef. 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 Montana

Similar in size to Great Barrier Reef

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