How to Measure Ring Size in MM UK – Complete 2026 Guide

How to Measure Ring Size in MM UK – 2026

The complete guide on how to measure ring size in mm — paper strip, string, existing ring & calliper methods, full UK mm size chart A–Z+2, diameter & circumference in mm, US & EU conversion & free calculator

🇬🇧 UK Sizes A – Z+2 📏 Measure in mm 📄 Paper Strip Method 💍 Existing Ring Method 🧮 Free MM Calculator ✅ 2026 Updated

53.8mm

📏 Average Women's
UK Ring Circumference

61.4mm

📏 Average Men's
UK Ring Circumference

÷π

🔢 Divide Circumference
by π to Get Diameter

±2mm

🌡️ Finger Size Varies
by Temperature

ℹ️

How to Measure Ring Size in MM – UK 2026 Overview

Measuring your ring size in millimetres (mm) is the most precise way to find your correct UK ring size. The UK uses a letter system (A to Z+2), but every UK size has an exact circumference in mm and inner diameter in mm. To measure ring size in mm at home, wrap a strip of paper or string around your finger, measure the length in mm, and match it to the circumference column in the chart below. The average UK women's ring circumference is 53.8 mm (UK N) and the average UK men's ring circumference is 61.4 mm (UK T). This guide covers all four measurement methods, key formulas, a full UK ring size chart in mm, and a free calculator.

How to Measure Ring Size in MM – At a Glance

Wrap a paper strip around your finger, measure it in mm — that is your circumference in mm. Divide by π (3.1416) to get the diameter in mm. Match either value to the UK ring size chart below. The best time to measure is evening, mid-afternoon — never when cold.

⭐ Women's avg: 53.8 mm ⭐ Men's avg: 61.4 mm 🔢 Circ ÷ π = Diameter 🌡️ Measure in the evening

🔍 How to Measure Ring Size in MM – 4 Methods UK

📄

Paper Strip Method

String or Dental Floss

No Tools Needed

Wrap non-stretchy string around your finger, mark the length, lay flat and measure in mm. Works identically to the paper method.

💍

Measure an Existing Ring

Most Accurate ⭐

Place a well-fitting ring on a ruler and measure its inner diameter in mm. Match to the Diam. (mm) column. No wrapping required.

📐

Digital Calliper

Precision ±0.1mm

Measure the inner diameter of an existing ring using a digital calliper for maximum precision. Best if you are between two UK sizes.

📄 Method 1 – How to Measure Ring Size in MM with Paper Strip

Paper Strip Method – Step by Step (Circumference in MM)

Cut a thin strip of non-stretchy paper

Cut a strip of printer paper approximately 10 cm long and 0.5 cm wide. Do not use tissue paper, cling film or foil — these stretch and give inaccurate readings.

Wrap it around the base of your ring finger

Wrap the strip snugly around the base of the finger you plan to wear the ring on. It should feel comfortably snug — not tight, not loose. Make sure it can still pass over the knuckle.

Mark the overlap precisely with a pen

Hold the strip in place and use a fine-tip pen or pencil to mark exactly where the end of the strip meets itself. A precise mark gives a precise measurement.

Measure the length in mm using a ruler

Lay the strip flat on a ruler. Measure from the starting edge to the pen mark in millimetres (mm). This figure is your finger circumference in mm. Write it down.

Match your mm measurement to the UK chart below

Find your circumference (mm) in the Circ. (mm) column of the chart below to identify your UK ring size. If between two values, always choose the larger size.

💡 Tip: Measure Three Times for Accuracy

Wrapping tension varies slightly each time you measure. Take three separate paper strip measurements in mm and use the average of the three. This significantly improves accuracy and reduces the chance of ordering the wrong ring size.

💍 Method 2 – Measure an Existing Ring in MM (Most Accurate)

How to Measure an Existing Ring's Inner Diameter in MM

Choose a ring that fits the correct finger well

Select a ring you already own that fits comfortably on the exact finger and hand you want the new ring for. Do not use a ring that is loose or tight.

Place the ring flat on a mm ruler or white paper

Lay the ring on a ruler with the inside facing upward, or trace the inner circle onto paper and measure the traced circle's diameter across its widest point.

Measure straight across the inside in mm

Measure the inside of the ring across its widest internal point in millimetres (mm). This is your inner diameter in mm. Use a digital calliper for precision to 0.1 mm.

Match diameter (mm) to the UK ring size chart below

Find your diameter measurement in the Diam. (mm) column of the chart below. Your UK letter size is in the same row. No further calculation is needed.

🔢 Ring Size MM Formulas – Diameter & Circumference

Circumference → Diameter (mm)

Diameter (mm) = Circumference (mm) ÷ 3.1416

Example: 53.8 mm ÷ 3.1416 = 17.12 mm = UK N (women's average)

Diameter → Circumference (mm)

Circumference (mm) = Diameter (mm) × 3.1416

Example: 19.56 mm × 3.1416 = 61.4 mm = UK T (men's average)

MM to Inches (if needed)

Inches = MM ÷ 25.4

Example: 53.8 mm ÷ 25.4 = 2.118 inches circumference = UK N

Between Two MM Values — Always

Choose the larger UK ring size

A ring that is slightly large is more comfortable and easier to resize down than a ring that is too tight.

🧮 Ring Size MM Calculator – Free UK Tool 2026

Enter your finger measurement in mm to find your UK ring size instantly

Your UK Ring Size

—

📊 Ring Size Chart in MM – Full UK A to Z+2 Reference (2026)

UK Size	Diam. (mm)	Circ. (mm)	🇺🇸 US Size	🇪🇺 EU Size	Diam. (inches)	Best For
A	11.9 mm	37.8 mm	—	37	0.469″	Children / XS
B	12.3 mm	39.1 mm	1	38	0.484″	Children / XS
C	12.7 mm	40.4 mm	1.5	40	0.500″	XS Women
D	13.1 mm	41.7 mm	2	41	0.516″	Small Women
E	13.5 mm	42.9 mm	2.5	42	0.531″	Small Women
F	13.9 mm	44.2 mm	3	43	0.547″	Small Women
G	14.3 mm	45.5 mm	3.5	45	0.563″	Women
H	14.7 mm	46.8 mm	4	46	0.579″	Women
I	15.1 mm	48.0 mm	4.5	47	0.594″	Women
J	15.5 mm	48.7 mm	4.75	48	0.610″	Women
K	15.9 mm	50.0 mm	5	49	0.626″	Women
L	16.3 mm	51.2 mm	5.5	50	0.642″	Women
M	16.7 mm	52.5 mm	6	51	0.657″	Women
N ⭐	17.1 mm	53.8 mm	6.5	52	0.673″	Women's Avg ⭐
O ⭐	17.5 mm	55.1 mm	7	54	0.689″	Women Popular
P ⭐	17.9 mm	56.3 mm	7.5	55	0.705″	Women Popular
Q	18.2 mm	57.2 mm	8	57	0.717″	Slim Men
R	18.6 mm	58.9 mm	8.5	58	0.732″	Lean Men
S	19.1 mm	60.2 mm	9	60	0.752″	Avg Slim Men
T ⭐	19.56 mm	61.4 mm	9.5	61	0.770″	Men's Avg ⭐
U ⭐	19.96 mm	62.7 mm	10	63	0.786″	Men Popular
V ⭐	20.37 mm	64.0 mm	10.5	64	0.802″	Men Popular
W	20.78 mm	65.3 mm	11	65	0.819″	Athletic Men
X	21.18 mm	66.6 mm	11.5	67	0.834″	Broad Men
Y	21.59 mm	67.8 mm	12	68	0.850″	Large Build
Z	21.79 mm	68.5 mm	12.5	69	0.858″	XL Build
Z+1	22.20 mm	69.7 mm	13	70	0.874″	XL Custom
Z+2	23.01 mm	72.3 mm	13.5	72	0.906″	Custom

⭐ UK N = average women's ring size — 53.8 mm circumference / 17.1 mm diameter

⭐ UK T = average men's ring size — 61.4 mm circumference / 19.56 mm diameter

📏 Circumference column = match your paper / string mm measurement here

💍 Diameter column = match your existing ring mm measurement here

📐 Band Width & MM Sizing – How Width Affects Your Ring Size

Why You Must Size Up in MM for Wider Ring Bands

A wider band covers more surface area of the finger and feels tighter than a narrow band at the same measured size. When measuring ring size in mm for a wide band ring, you must add mm to your measured circumference before matching to the size chart.

2–3 mm band

Order at your exact measured mm size — no adjustment needed

4–5 mm band

Order measured size or add ~1.6 mm to circumference (½ UK size up)

6–7 mm band ⭐ Most popular

Add approximately 1.6 mm to your circumference (½ UK size up)

8–9 mm band

Add approximately 3.1 mm to your circumference (1 full UK size up)

10–12 mm band

Add approximately 4.7 mm to your circumference (1½ UK sizes up)

✅ Top Tips When Measuring Ring Size in MM – UK 2026

7 Things That Affect Your Ring Size MM Measurement

🌡️ Temperature causes fingers to shrink or swell: Cold conditions reduce finger circumference by 1–2 mm. Heat causes swelling. Always measure at a comfortable room temperature, mid-afternoon when your fingers are at their normal resting size.
🕐 Best time to measure is evening: Fingers are at their largest in the evening and after physical activity. Goldsmiths UK recommends measuring in the evening for the most accurate result that accounts for natural daily swelling.
👉 Dominant hand fingers are larger: Your dominant (writing) hand is typically 0.5–1 UK size larger due to muscle development, which adds ~1.5–3 mm to the circumference. Always measure the specific finger and hand you plan to wear the ring on.
🔑 Always check the knuckle measurement in mm: If your knuckle circumference in mm is larger than your finger base, the ring must fit over the knuckle. Measure both — the base and the knuckle — and choose a size between the two mm measurements.
📏 Take three measurements and average: Paper wrapping tension varies. Three measurements and their average in mm gives the most reliable circumference reading and reduces errors by up to 1.5 mm.
💍 Add mm for wide bands: For bands 6 mm or wider, add 1.6–4.7 mm to your measured circumference before matching to the UK size chart (see band width guide above). Failing to do so is the most common cause of ordering a ring that is too tight.
↗️ If between two mm values on the chart, choose the larger UK size: A ring 1–2 mm too large in circumference can be resized or worn with a size adjuster. A ring even 1 mm too small in circumference will be uncomfortable and may be difficult to remove.

🏪

Want a 100% Accurate MM Measurement? Visit a UK Jeweller

All major UK high-street jewellers — including H.Samuel, Beaverbrooks, Goldsmiths, and Ernest Jones — will measure your ring finger in mm free of charge using a professional ring mandrel or ring gauge. For expensive rings (over £500) or rings made from non-resizable metals like tungsten or ceramic, always get professionally measured before ordering. A professional measurement takes under two minutes and is always free.

🌐 Trusted UK Ring Size MM References

🔗 Official UK Jeweller Guides – Ring Size in MM

Goldsmiths – How to Measure Ring Size in MM (Updated April 2026)

Beaverbrooks – Ring Size Guide with MM Chart UK

❓ How to Measure Ring Size in MM – UK FAQ 2026

What mm is the average UK women's ring size? ▾

The average UK women's ring size is UK N, which has a circumference of 53.8 mm and an inner diameter of 17.1 mm. Sizes L to O (circumference 51.2 mm to 55.1 mm) cover the majority of UK women. If buying a surprise gift with no size information, 53.8 mm (UK N) is the safest starting point.

What mm is the average UK men's ring size? ▾

The average UK men's ring size is UK T, which has a circumference of 61.4 mm and an inner diameter of 19.56 mm. Men's ring sizes typically range from UK Q (57.2 mm circumference) to UK W (65.3 mm circumference).

How do I measure ring size in mm with a ruler at home? ▾

Cut a thin paper strip, wrap it around your finger, mark the overlap, lay it flat, and measure the length in mm using a ruler. This gives your circumference in mm. Match it to the Circ. (mm) column in the chart above. Alternatively, measure the inner diameter of an existing ring in mm and match to the Diam. (mm) column.

My paper strip measured 61 mm — what UK size is that? ▾

A circumference of 61 mm is closest to UK T (61.4 mm), which is the UK average men's ring size. If you are between 60.2 mm (UK S) and 61.4 mm (UK T), choose UK T as the larger size for a comfortable fit.

Does ring size in mm change with temperature? ▾

Yes — fingers can change by 1–2 mm in circumference depending on temperature. Cold fingers shrink, warm fingers swell. Goldsmiths UK recommends measuring in the evening at a comfortable room temperature for the most reliable mm reading. Avoid measuring first thing in the morning or directly after coming in from the cold.

How do I convert my ring size mm to a UK letter size? ▾

Find your circumference in mm in the Circ. (mm) column of the chart above — the corresponding UK letter size is in the same row. If you have the diameter in mm, find it in the Diam. (mm) column. You can also use the free MM calculator on this page to get your UK size instantly.

What is the difference between ring diameter mm and ring circumference mm? ▾

Diameter (mm) is the straight-line measurement across the inside of the ring at its widest point. Circumference (mm) is the total distance around the inside of the ring — what you measure by wrapping paper around your finger. Circumference = Diameter × π (3.1416). For example, UK T has a diameter of 19.56 mm and a circumference of 61.4 mm.

Can I use a tape measure to find my ring size in mm? ▾

Yes — a soft tape measure (the type used in sewing or tailoring) works well. Wrap it gently around the base of your finger, ensure it is snug but not tight, and read the measurement in mm where it overlaps. This is your circumference in mm. Match this to the chart above. Make sure the tape passes over your knuckle comfortably as well.