Here is an example output for the Dickerson dodecamer (355d), which contains the reference for groove widths 3DNA uses. Specifically, read the two-page appendix of the 1998 El Hassan and Calladine paper.
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Minor and major groove widths: direct P-P distances and refined P-P distances
which take into account the directions of the sugar-phosphate backbones
(Subtract 5.8 Angstrom from the values to take account of the vdw radii
of the phosphate groups, and for comparison with FreeHelix and Curves.)
Ref: M. A. El Hassan and C. R. Calladine (1998). ``Two Distinct Modes of
Protein-induced Bending in DNA.'' J. Mol. Biol., v282, pp331-343.
Minor Groove Major Groove
P-P Refined P-P Refined
1 CG/CG --- --- --- ---
2 GC/GC --- --- --- ---
3 CG/CG 14.3 --- 18.2 ---
4 GA/TC 12.0 11.9 17.3 17.3
5 AA/TT 9.7 9.6 19.1 19.0
6 AT/AT 9.1 9.1 16.4 16.0
7 TT/AA 9.1 9.1 17.8 17.7
8 TC/GA 9.6 9.6 18.6 18.6
9 CG/CG 10.4 --- 19.0 ---
10 GC/GC --- --- --- ---
11 CG/CG --- --- --- ---
HTH,
Xiang-Jun