Physics dictates that the quality of sound produced is largely influenced by the length of the string. A longer string produces larger vibrations which not only make the sound louder, but also richer. The sound is then transmitted through the bridges and into the soundboard, which in turn acts like a loudspeaker to amplify the sound. Therefore, the longer the string and the larger the soundboard, the better the quality of tone produced.
The smallest upright piano normally measures around 108cm in height, with the largest instrument usually measuring as much as 132cm tall. The smallest grand piano generally measures 148–150cm (approx. 5’) in length, giving it almost equal string length and soundboard area to the largest upright model. The largest grand pianos measure up to 275cm in length (9’)