How to Measure Ring Size in CM – Complete Guide

How to Measure Ring Size in CM

Step-by-step guide to measuring your ring size in centimetres at home — using paper, string or an existing ring — then convert CM to AU, US, EU and all international sizes instantly

📏 Measure in CM 🔄 CM → AU / US / EU 🏠 3 Home Methods 🧮 Instant Calculator 💍 All Sizes A – Z+3

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Circumference or
Diameter in CM

✖️

×10

CM → MM
Multiply by 10

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4.75

Avg Women's
Circumference (cm)

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5.20

Avg Men's
Circumference (cm)

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What Does Measuring in CM Mean for Ring Sizing?

📐 CM Measurement Explained

Circumference in CM (Most Common Method)

Measure the distance around your finger in centimetres

Example: 4.75 cm circumference = 47.5 mm = AU Size N (most common women's size)

Diameter in CM (Existing Ring Method)

Measure straight across the inside of a ring in centimetres

Example: 1.51 cm diameter = 15.1 mm = AU Size N · 1.66 cm = 16.6 mm = AU Size T

CM → MM Conversion (Always Needed)

MM = CM × 10 | CM = MM ÷ 10

Ring size charts always use mm. Simply multiply your CM reading by 10 before looking it up.

Circumference → Diameter Formula

Diameter (cm) = Circumference (cm) ÷ 3.14159

Example: 4.75 cm ÷ 3.14159 = 1.512 cm diameter → AU Size N

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CM Ring Size Calculator

Enter your finger measurement in CM — get your AU, US, EU, Japan and India ring size instantly

Your AU / UK Ring Size

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3 Ways to Measure Ring Size in CM at Home

Method 1 — Most Accurate

📄 Paper Strip Method

Cut a thin paper strip

About 1 cm wide and 10 cm long. Tear or cut cleanly so the edges are straight.

Wrap around your finger base

Wrap snugly around the base of your intended finger. Make sure it can still slide past the knuckle.

Mark the overlap point

Use a pen to mark exactly where the paper overlaps itself. This is your finger circumference.

Measure in CM with a ruler

Lay the strip flat. Measure from the end to your pen mark in centimetres.

📏 Example: 4.75 cm = 47.5 mm → AU Size N

Method 2 — String / Thread

🧵 String Method

Cut a thin piece of string or thread

About 12–15 cm long. Thin cotton thread or dental floss works best — avoid stretchy materials.

Wrap around the finger

Wrap once snugly around the base of your finger, ensuring it passes over your knuckle.

Mark or pinch where it meets

Pinch the string at the exact point it meets itself, or use a pen to mark both pieces.

Lay flat and measure in CM

Place the string against a ruler and read the circumference in centimetres.

📏 Example: 5.20 cm = 52.0 mm → AU Size T

Method 3 — Existing Ring

💍 Existing Ring Diameter

Choose a well-fitting ring

Pick a ring that fits comfortably on the exact finger you want to size.

Place ring on a flat surface

Put the ring face-down on a flat table or piece of paper and trace around the inside.

Measure inner diameter in CM

Use a ruler to measure straight across the inside opening of the ring (inner diameter) in centimetres.

Convert to mm and look up chart

Multiply by 10 to get mm, then find in the Diameter (mm) column below.

📏 Example: 1.66 cm × 10 = 16.6 mm → AU Size T

Method 4 — Printable Sizer

🖨️ Printable Ring Sizer

Print at exactly 100% scale

Set printer to "Actual Size" — never "Fit to Page." Wrong scale = wrong size.

Verify the printed ruler

Check the printed 1 cm reference bar with a real ruler. If it measures exactly 1 cm, your print is correct.

Measure using the printed scale

Wrap the printed strip around your finger, read circumference in cm, then convert using the chart below.

Or place ring over printed circles

Lay your existing ring over the printed diameter circles to find your size directly.

⚠️ Always verify 1 cm reference bar first

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Finger Circumference in CM — Visual Scale

The typical range of finger circumferences for ring sizing. Most women's sizes fall between 4.0–5.0 cm and most men's sizes fall between 4.8–5.8 cm.

⚠️ Bar lengths are proportional to circumference for visual comparison only — not actual scale.

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Ring Size Chart — CM Circumference & Diameter

AU / UK	Circ. (cm)	Circ. (mm)	Diam. (cm)	Diam. (mm)	🇺🇸 US	🇪🇺 EU	Typical Wearer
A	3.78 cm	37.8 mm	1.20 cm	12.0 mm	0.5	38	Child
C	3.93 cm	39.3 mm	1.25 cm	12.5 mm	1.5	39	Child
E	4.08 cm	40.8 mm	1.30 cm	13.0 mm	2.5	40.5	Child
G	4.23 cm	42.3 mm	1.35 cm	13.5 mm	3.5	42	Small Women
I	4.38 cm	43.8 mm	1.39 cm	13.9 mm	4.25	43.5	Women
K	4.53 cm	45.3 mm	1.44 cm	14.4 mm	5.25	45	Women
L	4.60 cm	46.0 mm	1.46 cm	14.6 mm	5.5	46	Women
M	4.68 cm	46.8 mm	1.49 cm	14.9 mm	6	46.5	Popular ♀
N ⭐	4.75 cm	47.5 mm	1.51 cm	15.1 mm	6.5	47	Most Common ♀
O	4.83 cm	48.3 mm	1.53 cm	15.3 mm	7	48	Popular ♀
P	4.90 cm	49.0 mm	1.56 cm	15.6 mm	7.5	49	Unisex
Q	4.98 cm	49.8 mm	1.58 cm	15.8 mm	8	49.5	Unisex
R	5.05 cm	50.5 mm	1.61 cm	16.1 mm	8.5	50	Men
S	5.13 cm	51.3 mm	1.63 cm	16.3 mm	9	51	Men
T ⭐	5.20 cm	52.0 mm	1.66 cm	16.6 mm	9.5	52	Most Common ♂
U	5.28 cm	52.8 mm	1.68 cm	16.8 mm	10	52.5	Men
V	5.35 cm	53.5 mm	1.70 cm	17.0 mm	10.5	53	Men
X	5.50 cm	55.0 mm	1.75 cm	17.5 mm	11.5	55	Large Men
Z	5.65 cm	56.5 mm	1.80 cm	18.0 mm	12.5	56	Large Men
Z+3	5.88 cm	58.8 mm	1.87 cm	18.7 mm	14	58.5	XL

⭐ 4.75 cm = AU Size N = Most common women's size

⭐ 5.20 cm = AU Size T = Most common men's size

✖️ Always multiply CM × 10 to get mm

⬆️ Go up one size if between two measurements

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Common Mistakes When Measuring in CM

❌Confusing circumference and diameter — circumference is the distance around the finger (4.75 cm for Size N). Diameter is straight across the inside of the ring (1.51 cm for Size N). These are very different numbers — always confirm which you measured.
❌Forgetting to convert CM to MM — all ring size charts use millimetres. If you measure 4.75 cm, you must look up 47.5 mm, not 4.75. Simply multiply by 10.
❌Using a stretchy string or elastic — stretchy materials give a smaller-than-actual reading. Always use a non-stretch string, paper strip, or dental floss for accurate CM measurements.
❌Measuring in the morning — fingers are thinnest in the morning. Measuring then gives a size that may feel too tight by evening. Always measure in the afternoon or evening for the most accurate all-day fit.
❌Only measuring once — a single measurement can be off by 0.1–0.2 cm due to technique. Measure 3 times and average the results for accuracy. Even 0.1 cm = 1 mm, which can mean one full AU letter size difference.
❌Wrapping the paper too tightly or too loosely — the paper or string should sit snug against the skin but not compress it. It should feel like a comfortable ring, not a tourniquet or a loose bangle.
❌Not accounting for knuckle size — if your knuckle is larger than your finger base, the ring must pass over the knuckle daily. Measure over the knuckle too, and if larger, size for the knuckle and use a ring adjuster at the base.

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Expert Tips for Measuring in CM

🌇Measure in the evening — fingers reach their maximum size in the evening. Measuring then ensures your ring fits comfortably throughout the entire day.
✖️Always convert CM to MM for charts — multiply your CM reading by 10. Write down both values: e.g. 4.75 cm = 47.5 mm so you can easily cross-reference any size chart.
🔁Measure 3 times and average — record all three readings in cm, add them together and divide by 3. This eliminates variation from technique and gives the most reliable size.
📐Use the inside diameter for existing rings — when using a ring you already own, measure the inner diameter in cm and multiply by π (3.14159) to get the circumference, or look up the diameter directly in the cm column above.
⬆️Round up when between sizes — if your measurement of 4.82 cm falls between AU N (4.75 cm) and AU O (4.83 cm), always choose the larger size O for comfortable daily wear.
📏Wide bands feel tighter — size up — for any ring band 6 mm or wider, order one AU letter size larger than your measured CM size. Wide bands contact more of your finger surface and grip more tightly.

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Frequently Asked Questions

How do I measure my ring size in CM at home?▼

Cut a thin strip of paper about 1 cm wide and 10 cm long. Wrap it snugly around the base of your intended finger, mark where it overlaps, then lay it flat against a ruler. Read the length in centimetres — this is your finger circumference in CM. Multiply by 10 to get mm, then look it up in the chart above.

What is the average women's ring size in CM?▼

The average Australian women's ring size is AU Size N, which has a circumference of 4.75 cm (47.5 mm) and a diameter of 1.51 cm (15.1 mm). This equals US size 6.5 and EU size 47.

What is the average men's ring size in CM?▼

The average Australian men's ring size is AU Size T, which has a circumference of 5.20 cm (52.0 mm) and a diameter of 1.66 cm (16.6 mm). This equals US size 9.5 and EU size 52.

How do I convert CM to a ring size?▼

Multiply your CM circumference measurement by 10 to get millimetres. Then find that mm value in the Circumference (mm) column of the ring size chart above. For example: 4.75 cm × 10 = 47.5 mm = AU Size N. If between two sizes, always choose the larger size.

Is it better to measure circumference or diameter in CM?▼

For measuring your actual finger, circumference (wrapping around the finger) is easier and more accurate at home. For measuring an existing ring, diameter (measuring straight across the inside) is the easier method. Both work equally well — just make sure you use the correct column in the chart above.

My measurement is between two ring sizes in CM — which should I choose?▼

Always choose the larger size. A ring that is slightly too large can be worn with a ring adjuster, resized by a jeweller, or will feel fine throughout the day. A ring that is too small is uncomfortable, restricts circulation, and can be very difficult to remove — especially in warmer conditions when fingers swell.

Why do ring size charts show mm but my ruler shows cm?▼

Ring sizes internationally are standardised in millimetres for precision — even 0.5 mm can mean a full ring size difference. Most rulers show both cm and mm. Simply use the mm side, or measure in cm and multiply by 10. For example: 4.75 cm = 47.5 mm.