Estimating the correct nail length for solid tibial nails can be problematic. Most techniques reported in the literature for determining tibial nail length are not accurate. In a retrospective study of 16 patients in our unit, only three had ideal nail sizes. In these patients, as part of phase I of our study, we measured their normal leg's length from knee joint line to ankle joint line. An ideal nail length for each of these patients was estimated from a whole length radiograph of the nailed tibia. Comparing these two data, we found that deducting 20 mm from the leg measurement gave appropriate nail lengths. We also compared this with three other anthropometric measurements; tibial tuberosity to medial malleolus, joint line to medial malleolus and olecranon to head of V metacarpal head distance. The joint line to joint line measurement was the most reliable and showed the best correlation with ideal nail lengths (0.982). In phase II, a prospective study on 15 patients, we used the joint line to joint line measurement to determine nail sizes. A postoperative review of the radiographs showed all the nails to be of adequate length. This strengthened the fact that the joint line to joint line measurement is the most accurate and easy method to determine tibial nail lengths.