Every piece of body jewelry is described by three numbers: gauge for thickness, diameter for rings, and length for bars. Getting all three right is what separates jewelry that’s comfortable from jewelry that quietly causes trouble. Gauge runs on a backwards scale where a lower number means a thicker post, so 16 gauge (1.2mm) is chunkier than 20 gauge (0.8mm). What follows is the full sizing reference: the gauge-to-millimeter chart, typical sizes for every placement, and how to measure your own jewelry with calipers.
ℹ️ Good to know
Gauge runs on a backwards scale, where a lower number means a thicker post, so 16 gauge (1.2mm) is chunkier than 20 gauge (0.8mm).
Gauge to Millimeter Conversion Chart
Gauge is the number people get wrong most often, so it’s the place to start. The chart below covers the full standard range, from the thinnest fresh-piercing jewelry at 20 gauge down to stretched sizes at 00 gauge. Keep it handy when you’re ordering, because the millimeter value is what actually matters, and the gauge number is just shorthand for it.
| Gauge (g) | Millimeters (mm) | Inches (approx.) | Typical use |
|---|---|---|---|
| 20g | 0.8mm | 0.032″ | Thin nostril studs, some lobes |
| 18g | 1.0mm | 0.040″ | Nostril, lobe, some helix |
| 16g | 1.2mm | 0.047″ | Cartilage, septum, eyebrow, navel rings |
| 14g | 1.6mm | 0.063″ | Navel, tongue, nipple, industrial |
| 12g | 2.0mm | 0.080″ | Heavier nipple, first stretch |
| 10g | 2.4mm | 0.094″ | Stretched lobes, some heavy gauge work |
| 8g | 3.2mm | 0.128″ | Stretched lobes |
| 6g | 4mm | 0.160″ | Stretched lobes |
| 4g | 5mm | 0.200″ | Stretched lobes |
| 2g | 6mm | 0.236″ | Stretched lobes |
| 0g | 8mm | 0.312″ | Stretched lobes |
| 00g | 10mm | 0.394″ | Stretched lobes (scale ends here) |
Past 00g the gauge system runs out, and jewelry is simply labelled in millimeters or fractions of an inch: 12mm, 14mm, 1/2 inch, and up. The conversions above are the widely used industry values, though a few sellers round slightly differently, so when two charts disagree, trust the millimeter figure over the gauge label.
Gauge Explained: Lower Number, Thicker Jewelry
Gauge measures the thickness of the post, wire, or bar that passes through your piercing. The scale is inherited from old wire-manufacturing standards, where the number counted how many times the wire had been drawn thinner, so a higher number meant a thinner wire. That history is why the system feels backwards today.
In practice, a 20 gauge post (0.8mm) is thin, and the jewelry gets thicker as the number drops: 18g, then 16g, then 14g, and on down. If it helps, picture a flight of stairs going the wrong way, where every step down in number is a step up in thickness.
Your gauge isn’t a style choice. It’s set by the channel your piercer made. A healed fistula has a fixed diameter, and forcing a thicker post through it tears the tissue, while a thinner post leaves the channel loose enough to snag and irritate. Buy replacement jewelry in the exact gauge you were pierced at, and leave any change in gauge to a piercer doing a deliberate stretch.
Diameter Explained: The Inside of a Ring
Diameter is the spec for anything circular: seamless rings, captive bead rings, clickers, circular barbells, and hoops. The number you want is the internal diameter, the straight-line gap across the inside of the ring, not the outer edge. A ring sold as 8mm has an 8mm hole through the middle, and the metal sits outside that.
Diameter decides how a hoop sits against your body. Too large and it droops away from the skin, looking loose and catching on things. Too small and it pinches the tissue and can press on the piercing. The right diameter hugs the anatomy without squeezing it, which is why placement and your own proportions both feed into the number.
To measure a ring you already own, lay it flat and measure the inside distance straight across the widest point with calipers or a millimeter ruler. If you only have the ring on, measure from the inner edge of the entry hole to the inner edge of the exit. When you’re stuck between two sizes, your piercer can hold gauge-marked rings against the piercing and find the diameter that genuinely fits.
Length Explained: The Wearable Bar
Length is the spec for straight pieces: barbells, labret and flat-back studs, curved barbells, and circular barbell posts. It measures the wearable bar between the two ends, not including the balls, discs, or gems screwed onto either side. A 6mm flat-back has a 6mm post, and the disc and the top sit outside that measurement.
For a curved barbell, such as a navel or rook piece, length is measured along the curve rather than in a straight line. For a circular barbell or horseshoe, it’s the diameter rather than a straight length, measured the same way a ring is. Match the measuring method to the shape and you’ll order the right part.
Fresh piercings need extra length, and this trips people up constantly. A new piercing swells, so the initial bar is fitted long to leave room, often 2–3mm longer than the eventual size. Professional piercers, including the Association of Professional Piercers, fit that longer bar first and downsize to a snug one once the piercing has settled, so the jewelry doesn’t swing, snag, or let the tissue migrate around a post that’s too long. For the threading difference between bars, the threadless vs threaded breakdown covers which end style is easier to size and change.
Typical Sizes by Placement
These are the sizes piercers most often start with, but treat every figure as typical rather than guaranteed. Your anatomy, your piercer’s preference, and swelling all shift the numbers. Fresh-piercing lengths and diameters usually run a touch larger to allow for swelling, then downsize once healed.
| Placement | Typical gauge | Typical size | Common jewelry |
|---|---|---|---|
| Earlobe | 18g–20g (1.0–0.8mm) | 6–8mm post | Stud, flat-back |
| Helix / cartilage | 16g–18g (1.2–1.0mm) | 6–8mm post, 8mm ring | Flat-back stud, hoop |
| Conch | 16g (1.2mm) | 8mm post or larger | Flat-back stud, ring |
| Rook / daith | 16g (1.2mm) | 8mm curved bar / 8mm ring | Curved barbell, ring |
| Nostril | 18g–20g (1.0–0.8mm) | 6–8mm post, 8mm ring | Flat-back stud, hoop |
| Septum | 16g (1.2mm) | 8–10mm diameter | Circular barbell, clicker |
| Eyebrow | 16g (1.2mm) | 8–10mm curved bar | Curved barbell |
| Navel | 14g (1.6mm) | 10mm curved bar | Curved barbell |
| Tongue | 14g (1.6mm) | 16–19mm initial, downsize after swelling | Straight barbell |
| Nipple | 14g (1.6mm) | 12–16mm bar / ring | Straight barbell, ring |
| Industrial | 14g (1.6mm) | 32–38mm bar | Straight barbell |
| Lip / labret | 16g (1.2mm) | 8–10mm post initial | Flat-back stud |
The tongue line shows the swelling rule in action. A fresh tongue piercing is fitted with a long 16–19mm barbell because the tongue swells sharply in the first days, then it’s downsized to roughly 12–14mm once the swelling subsides, so the bar isn’t long enough to bang against your teeth. The initial size is rarely the size you keep.
How to Measure Your Own Jewelry
A cheap pair of stainless steel calipers makes every measurement above readable in seconds. Digital calipers display millimeters directly, which removes the guesswork of squinting at a ruler. Once you can read a piece, reordering stops being a gamble.
- Measure the gauge first. Close the caliper jaws gently on the post or wire, not the ball or disc, and read the millimeter value. Match that figure to the conversion chart above to get the gauge number.
- Measure a ring’s diameter inside. Lay the ring flat, open the calipers across the inside of the hoop at its widest point, and read the internal gap. That millimeter figure is the diameter you reorder by.
- Measure a barbell’s length along the bar. Measure only the wearable post between the two ends, straight across for a straight bar, along the curve for a curved one. Leave the balls and discs out of the measurement.
- Write all three down. Note the gauge, the diameter or length, and the placement together. That trio is everything a seller or piercer needs to match the piece exactly.
No calipers on hand? Any piercer will measure a piece for free and read off the gauge, diameter, and length, and they’ll flag if the size was wrong for the placement to begin with.
Some links below are affiliate links, and we may earn a small commission at no extra cost to you.
Why Correct Sizing Matters
Wrong size is one of the quietest causes of piercing trouble, because it doesn’t look like a mistake. The jewelry goes in, so people assume it fits. The problems show up over weeks as bumps, soreness, embedding, and migration that get blamed on aftercare instead of the bar. When a healed piercing stays irritated, healthdirect advises checking in with a health professional rather than waiting it out.
| Problem | What goes wrong | Result |
|---|---|---|
| Bar too short | The ends press into the tissue with no room for swelling | Pressure, embedding, and the disc sinking into the skin |
| Bar too long | Excess post lets the jewelry swing and snag | Tugging on the channel, irritation bumps, migration |
| Gauge too thick | The post is wider than the healed channel | Tearing the fistula when forced through |
| Gauge too thin | The post is narrower than the channel | Jewelry slides and shifts, irritating the walls |
| Ring diameter too small | The hoop squeezes the tissue it passes through | Pinching, pressure, and impeded healing |
| Ring diameter too large | The hoop hangs away from the body and catches | Snagging and constant downward drag |
The threaded end matters here too. A flat disc on the inside of a flat-back stud sits flatter against the tissue than a ball, which is part of why the flat-back vs ball-back choice affects comfort as much as size does. When the bar length and the end style both fit, the jewelry settles down and stops nagging at the piercing.
What to Avoid
These sizing missteps cause more irritation than any aftercare slip, so steer clear of all of them:
- Guessing your gauge instead of measuring it, since the backwards scale makes guessing unreliable
- Reordering a fresh-piercing length once you’re healed, when you should downsize to a snug bar instead
- Forcing a thicker post through a healed channel, which is tearing, not stretching
- Buying a ring by its outer size, because diameter is always the internal measurement
- Trusting the gauge label over the millimeter value when two charts disagree
- Sizing nipple or industrial bars by eye, since these placements vary widely and need measuring
Frequently Asked Questions
What does gauge mean in piercing jewelry?
Gauge is the thickness of the post or wire, and the numbering runs backwards, so a lower number means thicker jewelry. A 20 gauge post is 0.8mm thin, while a 0 gauge is 8mm thick. Lobes and nostrils sit in the thin range (18g–20g), cartilage and navels run thicker (14g–16g), and anything below 14g is stretched jewelry.
How do I convert gauge to millimeters?
The common conversions are 20g = 0.8mm, 18g = 1.0mm, 16g = 1.2mm, 14g = 1.6mm, 12g = 2.0mm, 10g = 2.4mm, 8g = 3.2mm, 6g = 4mm, 4g = 5mm, 2g = 6mm, 0g = 8mm, and 00g = 10mm. Once jewelry passes 00g, the gauge scale ends and sizes are listed in millimeters or fractions of an inch directly.
How do I measure the diameter of a ring or hoop?
Ring diameter is the internal measurement, the gap across the inside of the hoop, not the outer edge. Lay the ring flat and measure the inside distance straight across with calipers or a millimeter ruler. Common nostril and cartilage hoops run 6mm to 10mm internal diameter; septums often sit at 8mm to 10mm.
How do I measure barbell length?
Barbell length is the wearable post between the two ends, so measure the bar itself, not the balls or discs on either side. For a straight or flat-back bar, measure the straight section; for a curved barbell, measure along the curve. A fresh piercing needs extra length to allow for swelling, then you downsize to a snug fit once it has healed.
Why does correct jewelry size matter?
Jewelry that is too short presses on the tissue and can embed into the skin, while jewelry that is too long snags, swings, and tugs at the healing channel, and both cause irritation bumps and can drive migration. The gauge has to match the channel exactly too, since forcing a thicker or thinner post through a healed fistula tears it. Correct sizing is the single biggest comfort factor in jewelry that isn’t.
How do I find out the size of jewelry I already have?
Use a pair of calipers. Measure the post thickness for the gauge, the internal gap for a ring’s diameter, and the wearable bar for a barbell’s length, then compare the millimeter readings to a gauge chart. If you don’t own calipers, your piercer will measure any piece for free and tell you the exact gauge, diameter, and length.
Final Thoughts
Sizing comes down to three numbers, and once you can name them the rest falls into place. Gauge is thickness on a backwards scale, diameter is the inside of a ring, and length is the wearable bar. Measure each with calipers and match it to the chart.
The two rules worth carrying away: lower gauge means thicker jewelry, and fresh piercings wear longer bars that get downsized once they heal. A quality piece in the wrong size still causes problems, while the right size in a sound material sits comfortably and stays out of your way. If you’re buying for the long term, the gold piercing jewelry options follow the same gauge and length rules covered here, and the piercing aftercare guide covers keeping the piercing healthy once it fits.