Mean diameter: approximately 3,475 km · Orbits Earth.
Our own Moon ranks fifth, larger than Europa but smaller than Io. The dark patches visible from Earth are maria: plains formed by ancient volcanic activity, contrasting with the brighter highlands.
It is a familiar yardstick for the rest of this list. When comparing photographs, remember that the moons are shown at different image scales; their apparent sizes on the page do not represent their relative diameters.
Sources: NASA moon guide · JPL size data.
Image source: NASA/JPL/USGS; reuse terms. Resized and JPEG-compressed.