Top 10 countries with the longest coastline

The coastline measurement problem

Imagine measuring a bay with a ruler that skips its smaller curves. Using a shorter ruler captures more bends and produces a longer path. Repeating the process at finer scales changes the result again. Coastlines therefore need an operational measurement convention, including the map resolution and the features counted. A national figure made from a detailed chart cannot simply be compared with another country’s coarse outline and treated as evidence of a precise difference in real-world extent.

Islands change the comparison

An island-rich country adds many separate shorelines to its total. The puzzle includes island coasts, which helps explain why countries such as Indonesia, the Philippines and Japan feature in the answers. Canada and Norway also illustrate the importance of complex coast geometry. Land area does not predict coastal length: a relatively compact country can have a long, deeply indented shoreline. Measuring just the mainland edge would remove part of the coastline used by the original convention.

Why other published lists differ

NOAA distinguishes coastal and shoreline measurements and explains the chart conventions behind its US figures. That is useful evidence for why two totals can differ without either being a simple arithmetic error. The original CIA Factbook coastline link now redirects to a notice about the Factbook’s retirement, so it no longer supplies the saved comparative table. The archived order remains provisional while the historical source and its measurement conventions are recovered. The explanation remains available with the replay, but no new exact lengths or worldwide ratios are drawn from mixed sources with different scales.

Sources & further reading

• NOAA: how US shoreline length is measured
• CIA: World Factbook retirement notice

Explanation updated Thursday, October 1, 2026. The puzzle’s original data date is listed below.