Unless you specify the measurement when ordering, the danda will arrive oversized and need to be cut by you.

What to cut with?

It is easiest to cut with an electric mitre/chop saw, as it's possible to take off a small amount at a time until it's just right. It can also be cut with a hand saw or jig saw, but requires careful measuring, as it's more difficult to remove small amounts accurately. A bit of sandpaper and linseed oil (or vegetable oil) will tidy up the edge once it is the correct size.

How is the danda adjusted?

Swara danda

The pressure of the danda is adjusted by moving the base towards the hip and away from the hip. When the base of the danda is directly below the armpit (near the hip) there is maximum pressure. If the danda is long enough, it will be possible to move the base away from the hip to lessen the pressure. In practice, the danda is likely to be used somewhere between these two extremes.
Please note: If the danda is the correct length, the arm hangs comfortably, there is no contact between the elbow and the danda.

Japa Danda

Supporting the forearm during mantra japa is a matter of personal choice and experimentation. Ergonomically, having the shoulders level and the forearm parallel to the floor is likely to be the most comfortable position. Supporting the arm in this way also influences the swara.

How to measure?

Swara danda

1. Sit in your preferred meditation asana, using a cushion or however 'normal'.
2. Settle the body and then use a tape measure, with the help of a friend, to measure from the arm pit to the floor directly below. Also measure at a slight angle to the floor about 15cm away from hip. One measurement straight down and one at an angle. Cut danda to the longest measurement and then remove a bit more if it's too big.
3. If you'd like to use the danda in different asanas i.e. siddhasana (cross legged) and vajrasana (sitting on heels), then take measurements for each position and decide once you have an idea of all heights.

Japa danda

1. Sit in your preferred meditation asana, using a cushion or however 'normal'.
2. Settle the body, make sure the shoulders are soft and level.
3. Bend the elbow till your forearm is parallel to the floor. Use a tape measure, with the help of a friend, to measure from the forearm to the floor directly below. Cut danda as long as possible and then remove a bit more if it's too big.
   
4. If you'd like to use the danda in different asanas i.e. siddhasana (cross legged) and vajrasana (sitting on heels), then take measurements for each position and decide once you have an idea of all heights.

It is always best to cut it too long, test for size and then remove more rather than cut it too short in the first hasty cut!