How many strings does a standard grand piano have?

How to get close to this number

Multiply keys by strings per note. This site's companion question gives eighty-eight keys, and most notes are struck by two or three strings tuned together rather than one. Eighty-eight times an average of two and a half gives the answer, and the multiplier is the part people do not know.

The reason for multiple strings per note is volume and sustain. A single string cannot produce enough sound to fill a concert hall, so the upper registers use three strings per note struck simultaneously. The lowest notes use one thick wound string, which is why the multiplier is an average rather than a constant.

The tension figure in the explanation is what makes the instrument an engineering object: roughly twenty tonnes pulling on the frame. That is why a piano frame is cast iron and why a piano is so heavy — most of its mass exists to resist its own strings. An acoustic instrument that has to contain twenty tonnes of force is closer to a bridge than to a guitar.