The number of base pairs per turn is about 11, and the pitch of the helix of A-DNA is 2.46 nm.

In both A-DNA and B-DNA, the sugar moiety and base are on the opposite sides of the glycosidic bond. In the presence of high concentrations of cations, the nucleotides will rotate into syn-conformations. In these conditions, a different DNA conformation can exist. The chain zigzag of Z-DNA results in syn- and anti-conformations.

A-DNA appears when the DNA fibre (B-DNA) is dehydrated; that is, relative humidity is reduced from 92% to 75% and Na⁺, K⁺, and Cs⁺ ions are present in the medium. In other words, in solution, DNA assumes the B form and under conditions of dehydration, the A form.

Like B-DNA, A-DNA is a right-handed double helix, made of anti-parallel strands held together by Watson–Crick base pairing. But the vertical rise base pair is 2.3 Å, and the number of base pair per helical is 11, relative to the 3.4 Å rise and 10.4 base pairs per turn found in B-DNA. Such helix in A-DNA moves a total distance of (2.3 × 11) or 25.30 Å per turn, which is called the helix pitch. Obviously, the rotation per base pair A-DNA is 360/11 or 32.72 Å. The diametre of A-DNA helix is 25.5 Å, whereas that of B-DNA helix is 23.7 Å. The helix of A-DNA is, therefore, wider and shorter than that of B-DNA.