Ring Size Chart with Diameter

What Is Ring Diameter? — Illustrated Explanation

Inner diameter = the straight-line distance across the inside of a ring at its widest point. Measure with a mm ruler or digital calipers.

Ring Diameter Visual Scale — Proportional Circles UK A to Z+6

Each circle is drawn proportionally to the ring's inner diameter. Find your mm measurement and match to a circle. Gold = women's average (UK M, 15.9mm). Blue = men's average (UK T, 19.8mm).

🖨️ Printable Inner Diameter Reference — Place Existing Ring to Match

Print at 100% (no page scaling). Place your ring over each circle and match the inner edge to find your ring's inner diameter in mm. Best used with a metal or silver ring on white paper.

• 📐 Why diameter in mm is the most reliable home measurement: Inner diameter measured with digital calipers is the most reproducible ring size measurement — unlike a paper strip, calipers are rigid and do not stretch or compress. A £10 digital caliper from any hardware store reads to 0.1 mm precision, which is sufficient for ring sizing (one full UK letter size = 1.2–1.6 mm diameter increment). A ruler gives ±0.5 mm accuracy — still good enough to identify your size in most cases.
• 🔢 Diameter increments between UK ring sizes: Each full UK letter size = approximately 1.2–1.6 mm increase in inner diameter. Half-sizes add about 0.6–0.8 mm. Because the difference between adjacent sizes is small, always measure as precisely as possible. If your reading falls at 16.7 mm, you are precisely on UK Size M. At 16.1 mm you are between K½ and L. Enter the exact reading into the calculator to get the closest match.
• 🌡️ Does temperature change ring diameter? Yes — cold temperatures cause fingers to shrink and rings to sit looser; heat causes them to expand slightly. The diameter difference between a cold-morning finger and a warm-evening finger is typically 0.3–0.6 mm (roughly half a UK size). For rings worn all day (especially wedding bands), measure at a comfortable room temperature after light activity. Avoid measuring immediately after swimming, cold water or vigorous exercise.
• 💍 Measuring an existing ring's diameter for online ordering: If you need to reorder the same size or buy a matching ring for a different finger, always measure the existing ring's inner diameter rather than guessing. A ring that fits perfectly on your right hand's ring finger may be 1–2 sizes different from the left ring finger. Index fingers and middle fingers are typically larger than ring fingers — check each finger individually rather than assuming all fingers are the same diameter.
• 🛒 Using diameter when ordering from international websites: Many international online jewellers (particularly US, Chinese and European sellers) list ring sizes only in their local system. If you know your inner diameter in mm, you can convert to any country's size system using the calculator or chart above without any ambiguity. Always quote your diameter in mm in seller messages if asking about sizes — it is the one measurement that is universally understood regardless of the sizing system used.