The short answer: South Korea ranks 109th and North Korea 99th
First, the short answer. The National Atlas of Korea gives South Korea's area as 100,266 km², which ranks 109th in the world, and North Korea's as 123,138 km², which ranks 99th. The same source puts the entire territory of the Republic of Korea at 223,404 km², 85th among 253 countries worldwide.
No ratio comparing Korea's area with Japan's appears in the source material. Japan does turn up in the 2022 youth edition, in the explanation of standard time: the meridian used for Korean Standard Time is 135° east, the same one Japan uses, and that standard runs nine hours ahead of Britain. The atlas gives its area ratios against large countries such as Russia and Canada.
The main edition's page_413: 223,404 km² and 85th of 253 countries
Page_413, part of the main edition of the atlas, states the area in figures. The original text reads: "The area of the territory of the Republic of Korea is 223,404 km², which ranks 85th among the world's 253 countries." That sentence sits in the part of page_413 that explains area, with the figure and the ranking together in a single sentence.
The same page also breaks the total down into South Korea and North Korea. South Korea's 100,266 km² places it 109th in the world, behind Guatemala (108,889 km²) and Iceland (103,000 km²). North Korea covers 123,138 km², ranking 99th after Greece (131,957 km²) and Nicaragua (130,370 km²). Ten places separate the two.
Page_413 also lists countries of comparable size: the United Kingdom (243,610 km²) and Ghana (238,533 km²), along with Laos (236,800 km²) and Belarus (207,600 km²). All four sit close to 223,404 km².
The 2022 youth edition's page_3149: 220,950 km² and 84th of 218 countries
The 2022 youth edition uses different numbers. It puts the combined area of South and North Korea at 220,950 km², 84th among 218 countries worldwide, and South Korea's area at 100,410 km², suggesting Iceland (103,000 km²) and Cuba (110,860 km²) as comparisons.
Set the two documents side by side, item by item, and the differences stand out. The pages in question are page_413 of the main edition and page_3149 of the 2022 youth edition. The totals are 223,404 km² and 220,950 km²; the comparison sets, 253 countries and 218; the rankings, 85th and 84th. South Korea's area is 100,266 km² in one and 100,410 km² in the other.
The lists of similarly sized countries differ too. Page_413 names the United Kingdom, Ghana, Laos and Belarus, while page_3149 names the United Kingdom, Ghana, Romania (238,391 km²) and Laos. Page_3149 also describes where the country sits: a long, narrow peninsular nation between 124° and 132° east and between 33° and 43° north. The same page notes that the meridian for standard time is 135° east, as in Japan.
A world average of 541,424 km², a median of Togo at 56,785 km², and Russia 77.3 times larger
Page_413 of the main edition also gives the world average: the mean territorial area of the world's countries is 541,424 km², with Spain (505,370 km²) and Thailand (513,120 km²) offered as comparable cases. Botswana (581,730 km²), Yemen (527,968 km²) and Kenya (580,367 km²) appear on the same list. Measured against that average, 223,404 km² is a small figure.
The same page supplies a median as well. The country sitting at the midpoint of the area rankings is Togo (56,785 km²), with Croatia (56,594 km²) and Bosnia and Herzegovina (51,197 km²) as near neighbours, along with Costa Rica (51,100 km²) and Slovakia (49,035 km²). Take the median as the benchmark and the same area can arguably be read rather differently; an average, one might say, is easily pulled by very large countries.
Page_3149 of the 2022 youth edition sets out ratios against the biggest countries. Russia is 77.3 times the size of Korea's territory, Canada 44.7 times, the United States 44.5 times, China 43.5 times and Brazil 38.5 times. The page compares islands too: Greenland is about 9.6 times larger, Madagascar about 2.7 times.
From 220,109 km² in 1980 to 223,404 km² in 2013, with reclamation in the 1960s and 1970s
An area figure is not fixed once and for all. Page_413 of the main edition tracks the change: the territory of the Republic of Korea measured 220,109 km² in 1980 and reached 223,404 km² in 2013. Over the same period South Korea's area grew from 98,011 km² to 100,266 km², first passing 100,000 km² in 2010, at 100,033 km².
The same page discusses land reclamation, which in Korea has a long history as a way of securing farmland; the large-scale projects got under way in earnest in the 1960s and 1970s. The source material offers no figures tying the growth in area to those projects — only that the two explanations share a page.
In summary
So, back to the short answer. South Korea's area is 100,266 km², 109th in the world; North Korea covers 123,138 km², which ranks 99th. The whole territory comes to 223,404 km², 85th among 253 countries. No ratio comparing Korea's area with Japan's appears in the source material.
When citing an area figure, it is arguably safer to note which page it came from. Page_413 of the main edition and page_3149 of the 2022 youth edition differ in both the total area and the number of countries compared. You can open either page directly on the atlas website (nationalatlas.ngii.go.kr), where the original sentences are worth reading alongside the figures in parentheses.
