Most adults will use a full-sized cello known as a 4/4. Smaller adults and children should be fitted to a cello before buying or renting. Use the following steps to determine whether a cello is the correct playable size:

1. Sit on the edge of a chair and keep your feet flat on the floor. Your knees should be bent at a ninety-degree angle. If fitting a cello for a small child, try using an adjustable chair to make sure that they have their knees bent correctly while having their feet on the floor.

2. Adjust the endpin so that the top rounded part of the cello (or base of the fingerboard) touches the chest at the sternum (or breast bone). Your knees should touch the lower corner of the C bout. The C string peg should be close to the left ear.

3. Your hand should be able to easily touch the bottom of the fingerboard.