Each piano is given a serial number at “birth.” It’s usually located somewhere in the tuning pin area of the cast-iron plate, though sometimes it’s elsewhere, or difficult to find. See this illustration for typical locations. (If there appears to be more than one serial number on the piano, usually the longer one is the real serial number, the other being a number used by the factory during production.) If the manufacturer is still in business, it may be able to provide the year of manufacture from the serial number. Sometimes the information is on the manufacturer’s web site. For those not still in business, the Pierce Piano Atlas provides dates of manufacture from serial numbers for thousands of piano brands, both current and past. You can find the book through a piano technician or dealer, in libraries, or from www.piercepianoatlas.com. Where dates are not available in Pierce, or the serial number cannot be found, an experienced technician or rebuilder may be able to estimate the age of the piano from technical features or furniture design.
Many piano buyers make the mistake of thinking that dates found on the plate or soundboard, such as “Established 1837” or “Patented 1875,” represent the year of manufacture. They do not. The actual year of manufacture is almost never found on the piano, except as represented by the serial number.