The QWERTY keyboard has a wide form factor, whereas smartwatches frequently have round or square form factors. Even if extra space for an input field is considered, the aspect ratio of the QWERTY keyboard may not be optimal for a round or square smartwatch. We surmised that a narrower keyboard would be better able to utilize the screen area of a round or square smartwatch, thereby enabling larger keys and improved performance. Larger keys, however, may not necessarily result in better performance because of the reduced familiarity of a modified keyboard layout. To investigate this, we designed DiaQwerty keyboards, which are QWERTY variants with an aspect ratio of 10:7, and compared them with a plain QWERTY keyboard and a SplitBoard on round and square smartwatches. For a 33 mm round watch, DiaQwerty was comparable with QWERTY and was faster than SplitBoard. For a 24 mm x 30 mm square watch, DiaQwerty was faster than both QWERTY and SplitBoard. In the latter case, DiaQwerty achieved a 15% improvement over QWERTY. We concluded that the advantages of the enlarged keys outweighed the disadvantages of the reduced familiarity of the modified layout on a square watch.