Humidity refers to the amount of water vapor in the air.  Piano manufacturers suggest that the ideal humidity level for pianos is about 40 to 60 percent.  What is more important is the consistency of humidity.  One of the most important rule for good piano maintenance is keeping the humidity CONSTANT.

In North America, indoor humidity goes from very high to very low and back again. The swing in humidity causes alternate expansion and contraction.  This in turns can cause shrinking, cracking or warping even to wood that has been well seasoned prior to manufacturing.

It is therefore important to provide a continuous exchange of moisture between the air and the wood piano parts in the house, to attain a state of equilibrium. 

A HYGROMETER is a good way to measure the humidity in the air.

- mechanical, no batteries required
- 2" diameter
- inexpensive to own