How big is Ganymede?

Ganymede: 5,268 km (17,284,121 ft). Measured as diameter — mean diameter.

Where it sits

Among the 16 planets & moons on this page Ganymede ranks 9th from the top by size. The largest in the group is the Sun at 1,392,700 km, which is 264× the size of Ganymede, while the smallest, Ceres, is 939 km.

Stand an adult of 1.7 m beside it and the ratio is 3,098,941×: you would need 3,098,941 people stacked head to foot to match its width — roughly a crowd the size of a small town standing on each other.

In everyday distances

A football pitch is about 105 m long. Ganymede is 50,173× that, which puts it at 50,173 pitch lengths from end to end.

Light covers its diameter in 18 milliseconds. A jet cruising at 900 km/h would need 5.9 hours to fly the same distance in a straight line.

Next to its neighbours in size

The nearest thing larger than it in this collection is Mars at 6,779 km (22,240,814 ft), 1.29× the size. Both figures are the same kind of measurement, so the gap is a fair one.

The nearest thing smaller is Titan at 5,149 km (16,894,357 ft), so Ganymede is 1.02× as big as it. They sit in the same group.

Against fixed yardsticks

Against three fixed yardsticks — Ganymede is 15,964× the size of Eiffel Tower (330 m); Ganymede is 176,194× the size of blue whale (29.9 m); Earth (12,742 km) is 2.42× the size of Ganymede.

How this figure was taken

Worlds are listed by diameter. Gas giants are not round, so equatorial diameter is used for them and mean diameter for the rest. All figures are rounded from published mission data.

How the sizes are taken. Each figure says what it measures — height, length, diameter or elevation — and for which individual or convention. Everything is drawn standing upright on one baseline so a single scale holds, including things that are long rather than tall. Values come from the linked Wikipedia article for each item.

Read the rest — common questions