Simple cubicAn atom at each corner only. One atom in all belongs to the cell.
Body-centered cubicCorner atoms plus one in the center. Two atoms in all belong to the cell.
Face-centered cubicCorner atoms plus one on each face. Four atoms in all belong to the cell.
Corner atomIt is shared by eight cells, so one-eighth of it counts here.
Cell edgeOne edge of the cube. All edges of a cubic cell are equal.
Body-center atomIt lies wholly inside the cell and has eight nearest neighbors.
Body diagonalA line from one corner to the opposite corner, through the center.
Face diagonalA line across one face from corner to opposite corner.
Face-center atomIt is shared by two cells, so half of it counts here.
How this list was compiled: Every name and count checked on 2026-10-01, kept only where two independent sources agree. (1) Purdue University, Bodner Research Web, Unit Cells, https://chemed.chem.purdue.edu/genchem/topicreview/bp/ch13/unitcell.php (unit cell, lattice points, simple cubic, body-centered cubic and face-centered cubic; a corner atom is shared by eight cells and a face atom by two; 1, 2 and 4 atoms per cell; cell-edge length; the diagonal across the body). (2) Florida State University, General Chemistry II notes, Solids, https://www.chem.fsu.edu/chemlab/chm1046course/solids.html (unit cell; corner spheres one-eighth inside; coordination number six for simple cubic and eight for body-centered cubic; face diagonal and body diagonal; atoms touch along the body diagonal; few metals are simple cubic). (3) Wikipedia, Cubic crystal system, text only, https://en.wikipedia.org/wiki/Cubic_crystal_system (net lattice points per cell 2 and 4; coordination numbers 6, 8 and 12; primitive cubic rare). Licence: own work
The drawing: Drawn for this site on 2026-10-01 from plain geometry; nothing traced. Licence: own work
How it works
The middle cube is the body-centered cubic (bcc) unit cell. The simple cubic cell is on its left and the face-centered cubic (fcc) cell on its right. Tap a numbered ring to see a name.
Read the full guide
Where the atoms sit
A unit cell is a crystal's simplest repeating unit. All three cells have an atom at each of the eight corners. Simple cubic has no others. Body-centered cubic adds one atom in the center of the cube. Face-centered cubic adds one in the center of each of the six faces.
Counting the atoms in one cell
A corner atom is shared by eight cells, so one-eighth of it belongs to each. A face atom is shared by two. The body-center atom is not shared. That gives 1 atom for simple cubic, 2 for body-centered cubic and 4 for face-centered cubic.
The atoms are drawn small so you can see inside. In body-centered cubic the atoms touch along the body diagonal.
Questions and answers
How many atoms are in a bcc unit cell?
Two. The eight corner atoms each count for one-eighth, which makes one, and the atom in the center of the body counts whole.
What is the coordination number of a bcc unit cell?
Eight. The atom in the center has the eight corner atoms as its nearest neighbors. In simple cubic the coordination number is 6 and in face-centered cubic it is 12.
What is the difference between bcc and fcc?
Body-centered cubic has one extra atom in the center of the cube. Face-centered cubic has no atom there; it has one in the center of each face instead, giving four atoms per cell.
Which cubic unit cell is the least common?
Simple cubic. It uses space inefficiently, so few metals adopt it, and it is rare in nature.