When earring stores list “18g” or “1.0 mm” they are describing the thickness of the post that passes through the piercing. Get it wrong and the earring either will not go in or sits loose and irritates. The gauge scale is old and counter-intuitive, because a bigger number means thinner wire. This calculator converts a gauge to millimetres and inches, or finds the nearest gauge for a post you measured.
How to use the earring gauge calculator
- Choose what you know. Pick “The gauge” if the packet or your piercer gave you a number such as 16g, or “The thickness of the post” if you measured it.
- Select the gauge, or enter the thickness in millimetres, inches or centimetres. Use calipers for an accurate reading.
- Read the result: the gauge, the diameter in millimetres and the diameter in inches. For a measured post, the nearest gauge is shown.
Earring gauge formula
diameter (in) = 0.005 × 92(36 − gauge) ÷ 39
Body jewellery uses the American Wire Gauge (AWG) scale (Wikipedia, “Body jewelry sizes” and “American wire gauge”, retrieved 2026-10-16). The table below uses the published values, which the article rounds a little differently from the formula for some sizes. Fractional inch sizes are included as the article lists them.
| Gauge / size | Decimal inches | Millimetres |
|---|---|---|
| 20g | 0.0320 | 0.812 |
| 18g | 0.0403 | 1.024 |
| 16g | 0.0508 | 1.291 |
| 1/16" | 0.0625 | 1.588 |
| 14g | 0.0641 | 1.628 |
| 12g | 0.0808 | 2.05 |
| 10g | 0.1019 | 2.58 |
| 1/8" | 0.1250 | 3.18 |
| 8g | 0.1285 | 3.26 |
| 6g | 0.1620 | 4.12 |
| 3/16" | 0.1875 | 4.76 |
| 4g | 0.204 | 5.19 |
| 1/4" | 0.250 | 6.35 |
| 2g | 0.258 | 6.54 |
| 5/16" | 0.312 | 7.94 |
| 0g | 0.325 | 8.25 |
| 00g | 0.365 | 9.27 |
| 3/8" | 0.375 | 9.52 |
| 000g | 0.410 | 10.4 |
| 7/16" | 0.438 | 11.11 |
| 0000g | 0.460 | 11.68 |
| 1/2" | 0.500 | 12.7 |
Published values compared with the AWG formula
| Gauge | AWG formula (mm) | Published (mm) |
|---|---|---|
| 20g | 0.812 | 0.812 |
| 18g | 1.024 | 1.024 |
| 16g | 1.291 | 1.291 |
| 14g | 1.628 | 1.628 |
| 12g | 2.053 | 2.05 |
| 10g | 2.588 | 2.58 |
| 8g | 3.264 | 3.26 |
| 6g | 4.115 | 4.12 |
| 4g | 5.189 | 5.19 |
| 2g | 6.544 | 6.54 |
| 0g | 8.251 | 8.25 |
| 00g | 8.251 | 9.27 |
| 000g | 8.251 | 10.4 |
| 0000g | 8.251 | 11.68 |
Worked example
You measure a stud post with calipers and find it is 1.2 mm thick.
- 16g is 1.291 mm, a difference of 0.091 mm.
- 18g is 1.024 mm, a difference of 0.176 mm.
- The nearest size is 16g (0.0508 in). Because 1.2 mm is between sizes, ask the seller for the exact diameter before buying.
Tips for choosing earring sizes
- Stay the same or larger. A thinner post than the piercing can slide and irritate, while a thicker one may not pass.
- Do not force it. If an earring will not go through, check the gauge rather than pushing.
- Calipers are better than a ruler. The difference between 18g and 16g is only 0.27 mm.
- Hoops have two measurements. The wire gauge is the thickness and the inner diameter is the hoop size, usually in millimetres.
This tool gives chart values and is not medical advice. For other jewellery sizes try the Ring Size Calculator, Bangle Size Calculator and Glasses Size Calculator.
Sources
Every figure above comes from these pages, read directly on the date shown. Brand names are used only to identify published guides.
- Wikipedia — Body jewelry sizes (gauge table in AWG, inches and millimetres) — retrieved 2026-10-16
- Wikipedia — American wire gauge (diameter formula) — retrieved 2026-10-16
Frequently asked questions
What does gauge mean for earrings?
Gauge is a way of naming the thickness of the post or wire. Body jewellery uses the American Wire Gauge scale, where a larger gauge number means a thinner wire. 20g is 0.812 mm and 0g is 8.25 mm.
What is the standard earring gauge?
Most ear lobe piercings are made at 20g, 18g or 16g, which is 0.812, 1.024 and 1.291 mm. Cartilage piercings are often 16g or 18g. Your piercer will say which size your piercing was made at, and you should keep jewellery the same size or larger.
How do I convert gauge to millimetres?
Use the American Wire Gauge formula d = 0.127 mm × 92^((36 − n) ÷ 39), where n is the gauge number. For 16g this gives 1.291 mm. Published body jewellery charts round several values, for example 12g is 2.05 mm.
Why are there fractions of an inch in the chart?
Above about 0g, stretched piercings are measured in fractions of an inch or in millimetres rather than gauge. The chart includes 1/16 in, 1/8 in, 3/16 in, 1/4 in, 5/16 in, 3/8 in, 7/16 in and 1/2 in so you can compare them with the nearest gauge.
How do I measure my earring post?
Measure the diameter of the post or wire with calipers or a micrometre, as a ruler is not precise enough for 1 mm. Then use the second method of this calculator, which finds the closest gauge. See the Ring Size Calculator and Bangle Size Calculator for other jewellery measurements.