Quick answer: Most small-to-medium bongs use 14.5 mm joints. Larger, high-airflow setups often use 18.8 mm. Your new bowl/downstem must match the joint size (or you’ll need an adapter).
What the numbers mean
- The size refers to the glass-on-glass joint diameter.
- For a female joint on your bong, the number is the inner diameter of that socket.
- For a male piece (like a bowl or downstem), the number is the outer diameter of the ground glass.
So a 14.5 mm male bowl fits a 14.5 mm female joint, and the same for 18.8 mm.
Tip: Angle (45° vs 90°) and joint gender are separate from size. You need all three: size + gender + angle.
How to check your size in 30 seconds
- Look at the joint: If the bong opening is a socket, it’s female. If a piece sticks out, it’s male.
- Measure: Use a ruler or caliper across the diameter of the joint area.
- Around 14–15 mm on the ruler → it’s 14.5 mm.
- Around 18–19 mm on the ruler → it’s 18.8 mm.
- Match the piece: Buy bowls/downstems that exactly match your joint size and gender.
Which one should you pick?
14.5 mm — compact and versatile
- Tighter airflow for snappier hits and smaller chambers
- Great for daily drivers, mini bongs, and beginners
- Wider selection of small bowls and quartz bangers
18.8 mm — bigger airflow, bigger pieces
- Freer pull for large percs and tall tubes
- Better for massive rips and heavy diffusion
- Sturdier feel for large bowls and robust downstems
Adapters save the day
Already have a favorite bowl but the size doesn’t match? Grab an adapter:
- 18.8 → 14.5 lets you use smaller bowls on a large joint
- 14.5 → 18.8 lets you use large pieces on a small joint
- Also available in male→female and female→male combos
FAQs
Does 18.8 mm always hit “harder”?
Not automatically. It moves more air more easily, which pairs well with bigger percs and chambers. But bowl size, water level, and percs matter just as much.
Will a 14.5 mm bowl work in an 18.8 mm joint?
No. It will be too small and air will leak. Use an 18.8 → 14.5 adapter.
What if I’m still unsure?
Snap a clear photo of your joint next to a ruler and compare to the measurements above—or bring the bong to the shop and test-fit.
Ready to kit it out?
Browse our essentials and match your size:
- Bowls & Slides — shop 14.5 mm and 18.8 mm options
- Downstems & Adapters — fix mismatches and upgrade airflow
- Quartz Bangers — pick by size and angle (45°/90°)
Want help choosing? Send us a message with your bong photo and we’ll point you to the exact fit.
