Why Piercing Gauge Runs Backwards
Body jewellery gauge runs backwards from every other measurement people are used to: a higher number means a thinner bar. A 20g nose stud is 0.8 mm; a 0g plug is 8 mm, ten times thicker.
Where the backwards scale comes from
It descends loosely from American Wire Gauge, where the number counted the drawing operations a wire went through — more passes meant a thinner wire and a higher number. Body jewellery inherited the direction and then rounded each size to a convenient millimetre value, so the gauge converter uses the published body-jewellery chart rather than the raw AWG formula.
Above 00g the convention gives up entirely and jewellery is sold in plain millimetres or inches, which is why the chart stops there.
The steps are not even
This is the practical consequence, and it matters most for stretching:
- 20g = 0.8 mm, 18g = 1.0, 16g = 1.2, 14g = 1.6
- 12g = 2.0, 10g = 2.4, 8g = 3.2
- 6g = 4, 4g = 5, 2g = 6, 0g = 8, 00g = 10
At the thin end the steps are 0.2 to 0.4 mm. At the thick end, 2g to 0g is a 2 mm jump and 0g to 00g another 2 mm. The same “one size” means five times as much tissue change at the top of the scale as at the bottom.
Common sizes by placement
Most standard piercings sit in a narrow band. Lobes and nostrils are commonly 20g to 18g; most cartilage and navels are 16g to 14g; nipples and septums are often 14g. Larger gauges are stretching territory rather than starting sizes.
Anatomy matters more than the convention, though. Some piercers prefer heavier jewellery in cartilage on the grounds that a thicker bar is more stable and less prone to irritation, and a well-fitted 14g is often better tolerated than a thin one that moves.
Do not shop by number alone
Two things go wrong. First, some retailers quote gauge and millimetres inconsistently, and a mismatch of one size is enough that jewellery will not go in — or will go in loosely, which is worse.
Second, gauge describes only thickness. A barbell also has a length and a ball size, and a ring has an internal diameter. Ordering the right gauge in the wrong length is the most common body-jewellery mistake, and the jewellery size calculator exists because of it.
Measure the jewellery you have
If you already wear something that fits, the reliable move is to measure it rather than to guess the gauge from a product page. Calipers are cheap; the converter turns a millimetre reading back into a gauge and an inch equivalent.
Measure the bar itself, not the decorative end — a 16g bar can carry a much larger ball, and people frequently report the ball's size by mistake.
Inches are a third system
Stretched sizes are widely quoted in inches, and the fractions do not correspond neatly to the gauge numbers. The converter reports all three because sellers use all three, sometimes on the same page.
When ordering across markets, the millimetre figure is the one to trust. It is a measurement; the other two are conventions.