Twelve is a composite number with proper divisors 1, 2, 3, 4 and 6.

12 is an abundant number since the sum of its proper divisors (1 + 2 + 3 + 4 + 6 = 16) is greater than itself.

Twelve is a sublime number, a number that has a perfect number of divisors (6), and the sum of its divisors is also a perfect number (28).

Also:

• A dodecagon has 12 sides
• A cube and an octahedron have 12 edges
• A dodecahedron, an octahemioctahedron, a pentagonal antiprism, a pentagrammic antiprism, and a pentagrammic crossed-antiprism have 12 faces
• A truncated icosahedron, an icosidodecahedron, a rhombicosidodecahedron, a ditrigonal dodecahedron, a great ditrigonal icosidodecahedron, a small dodecahemidodecahedron, a quasitruncated small stellated dodecahedron, a great dodecahemicosahedron, a snub dodecadodecahedron, a snub icosidodecadodecahedron, and an inverted snub dodecadodecahedron have 12 pentagons
• A truncated cuboctahedron, a small rhombihexahedron, a quasitruncated cuboctahedron, and a great rhombihexahedron have 12 squares
• An icosahedron, a truncated tetrahedron and a cuboctahedron, a small stellated dodecahedron, a great dodecahedron, a great icosahedron, a tetrahemihexahedron, and a cubohemioctahedron have 12 vertices
• A small stellated dodecahedron, a great dodecahedron, a great stellated dodecahedron and a ditrigonal dodecahedron, a small ditrigonal icosidodecahedron, a small icosicosidodecahedron, a dodecadodecahedron, a truncated great dodecahedron, a great ditrigonal dodecicosidodecahedron, a great icosicosidodecahedron, a great icosidodecahedron, a truncated great icosahedron, a quasitruncated small stellated dodecahedron, a great dodecicosidodecahedron, a small dodecahemicosahedron, a great dodecahemidodecahedron, a small snub icosicosidodecahedron, a snub dodecadodecahedron, a snub icosidodecadodecahedron, a great snub icosidodecahedron, an inverted snub dodecadodecahedron, a great inverted snub icosidodecahedron, a great inverted retrosnub icosidodecahedron, and a small inverted retrosnub icosicosidodecahedron have 12 pentagrams
• A great ditrigonal dodecicosidodecahedron, a quasitruncated dodecahedron, a great dodecicosidodecahedron, a great dodecicosahedron, a quasitruncated great stellated dodecahedron, a quasirhombicosidodecahedron, a great quasitruncated icosidodecahedron, and a great rhombidodecahedron have 12 decagrams
• A small dodecicosidodecahedron has 12 triangles
• A truncated dodecahedron, a small dodecicosidodecahedron, a small rhombidodecahedron, a truncated great dodecahedron, a small dodecicosahedron, and a quasitruncated dodecahedron have 12 decagons
• 12 is pentagonal number
• 12 is a pronic number.