While it has been established previously that the strengths of commercial timber products containing knots and other natural growth characteristics are greatly influenced by the physical dimensions of the pieces, it has not been established whether the same is the case for defect-free wood. The structural engineer has a choice of many grades of timber available for his designs and it may be argued that these grades form a stepwise progression from the rather weak No. 3 grade through select structural grade and into clear defect-free sawn wood. For efficient design, it is important to have the size effects correctly quantified for the different qualities. This study concentrates on quantifying the size effect at the strong end of the perceived progression of increased strength, the clear defect-free wood. For the bending tests carried out in this study, it was found that the length effect was very pronounced while thickness did not affect strength. A consistent depth effect could not be found. If some dept...