Instruments are designed and tuned to a specific pitch. The pitch is the proportional relation to the tuning tone A. The standard pitch in Europe is 442/443Hz, in the US and England 440Hz at 20 Celsius or 68-70F
There are certain things to keep in mind:
The pitch depends also on the room as well as instrument temperature. The pitch will go up as warmer the instrument becomes.
Clarinets are supplied with one and sometimes two barrels. The length of the barrel has a significant influence on the pitch. An instrument pitch can be altered by about 2 Hz by using a different barrel, but a change of barrel length will always have a bigger influence close to the barrel then for the notes further away. It can be a good idea to combine a different barrel with an intonation ring.