Transpedicular spinal fixation is a widely used method in vertebral surgery, but it suffers from complications due to mismatches between the screw and pedicle. Therefore, information on minimal cancellous (MCD) and minimal external diameters (MED) of the pedicle is highly important for vertebral surgery. To determine these diameters and their ratios, 2,808 measurements of 1,404 pedicles of 702 human vertebrae were made from Th11 to L5. We found that the mean ratio of MCD to MED was 72.2%, MCD to vertical diameter (VD) was 41.7%, and MCD to transverse diameter (TD) was 62.2% in all levels. We recommend that these results be considered prior to pedicular fixation operations and design of new implantable devices.