How to Figure Out the Bong Size of Your Downstem

Choosing the right bowl piece and downstem for your bong can seem like a daunting task, but it doesn’t have to be! With a few simple tips, you’ll be able to select a bowl piece and downstem that will fit your bong perfectly.


We’ll provide information on the different types of bowl pieces and how to measure the size of your downstem, as well as advice on how to select a downstem that is the right size for your bowl piece.

What Size Downstem Do I Need?

There are two main factors that need to be taken into account: Length and Diameter.


  • The length of your downstem should be measured from the tip of the stem to the end of the ground joint in order for it to enter the water chamber without hitting the bottom.
  • The diameter is what determines how much smoke passes through your piece; if you have a 10mm joint, you’ll get less smoke than you would with an 18mm joint.


To help you figure out which size downstem is best for your bong, we recommend measuring the circumference of your piece and dividing by 3.14 (pi). The resulting number will give you your ideal diameter. You can then use the table below as a guide:


Joint Size Circumference (in mm) Approximate Finger Width
10mm 31.4mm Very Small
14mm 44.2mm Same size as your pinky finger
18mm 56.5mm Same size as your thumb


As you can see:


  • 10mm joints are very small and usually easily discernible to those familiar with the other two joint sizes.
  • 14mm downstems should be about the same diameter of your pinky finger;
  • 18mm stem will be about the size of your thumb.


If you want to get more precise measurements, measure the circumference of your glass and divide by 3.14 for an exact diameter size.

Male vs Female Bowl Piece

Bowl pieces come in two main varieties: male and female.


  • Male bowl pieces are larger, usually used with an 18mm downstem and fit directly into the bong’s joint.
  • Female bowl pieces slide into the downstem and are secured using a rubber or metal grommet.


The size of your bowl piece should correspond to your downstem size – 10mm for a 10mm downstem, 14mm for a 14mm downstem, etc. Most standard bongs use either 10 or 14 mm bowls, while larger bongs often use an 18mm bowl piece.

How to Measure Downstem Size

Measuring your downstem size is relatively simple. Just take a ruler and measure the diameter of the joint where it attaches to the bowl piece or water chamber. This will give you an accurate measurement that you can use when selecting a new downstem.

Choosing the Right Downstem for Your Bowl Piece

When selecting a new downstem, you’ll first need to measure the size of your existing bowl piece. Then look for a downstem that matches the same size as your male or female bowl piece.


For example, if you have a 10mm male bowl piece, then you’ll need a 10mm downstem. The same goes for larger bongs – just make sure the sizes match up correctly!