| Rank | Island | In Japanese | Area (km²) | Prefecture |
|---|---|---|---|---|
| 1 | Honshu | 本州 | 227,942.76 | |
| 2 | Hokkaido | 北海道 | 77,982.32 | |
| 3 | Kyushu | 九州 | 36,781.68 | |
| 4 | Shikoku | 四国 | 18,296.12 | |
| 5 | Etorofu | 択捉島 | 3,166.64 | Hokkaido (boundary not fixed) |
| 6 | Kunashiri | 国後島 | 1,489.27 | Hokkaido (boundary not fixed) |
| 7 | Okinawa Island | 沖縄島 | 1,208.49 | Okinawa |
| 8 | Sado | 佐渡島 | 854.81 | Niigata |
| 9 | Oshima (Amami) | 大島 | 712.42 | Kagoshima |
| 10 | Tsushima | 対馬 | 695.74 | Nagasaki |
In the GSI’s list of islands by area (as of April 1, 2026), Honshu comes first at 227,942.76 km², then Hokkaido at 77,982.32 km², Kyushu at 36,781.68 km² and Shikoku at 18,296.12 km².
By our own calculation, Honshu is about 2.9 times the size of Hokkaido.
After these four, the list includes Etorofu (3,166.64 km²) and Kunashiri (1,489.27 km²), which the GSI lists under Hokkaido with their boundaries not yet fixed, then Okinawa Island (1,208.49 km²), Sado (854.81 km²), Oshima in Amami (712.42 km²) and Tsushima (695.74 km²).
The GSI measures the area of every lake and island of 1 km² or more, and lists them at the end of its survey of the areas of prefectures and municipalities.
In 2023, the GSI counted the islands of Japan on its detailed digital map and found 14,125.
There is no single right answer. Talking it over with someone at home is a good way to learn.