The DNA double-helix can form somewhat different three-dimensional conformations depending on environmental conditions and, to some extent, on the base sequence. Inside the cell where the DNA is fully hydrated, a highly regular structure known as the B-form is adopted. The diameter of the B-DNA is 20 angstroms, and the distance between base pairs is 3.4 angstroms. Since each helix has 10 bp the length is approximately 34 angstroms.