How to Measure Ring Size With String – Step-by-Step Guide

How to Measure Ring Size With String

Step-by-step guide to measuring your ring size accurately using string or dental floss at home — includes the best string types to use, common mistakes, size chart, calculator and expert tips

🧵 String & Floss Methods 📏 5-Step Instructions ✅ Do's & Don'ts 🧮 Instant Calculator 🇦🇺 AU · 🇺🇸 US · 🇪🇺 EU Chart 💡 Expert Tips

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Simple Steps
String Method

⏱️

2 min

Time Needed
to Measure

📐

Always Measure
in Millimetres

🔁

×3

Measure 3 Times
and Average

The string method is one of the most popular ways to measure ring size at home because it requires no special tools — just a piece of non-elastic string, thread, or dental floss, a pen, and a ruler. Wrap the string around the base of your finger, mark where the ends meet, lay it flat, and measure the length in millimetres. That measurement is your inner circumference, which you match to a ring size chart. The most important rule: always use non-stretchy material — elastic string compresses and gives a smaller reading than your true size.

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Best Types of String to Use

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Dental Floss

The #1 recommended material. Non-elastic, thin, consistent width, and available in almost every home. Glides over the knuckle smoothly without bunching.

✓ Best Choice

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Cotton Thread

Works well if it is a single, fine thread pulled taut. Avoid thick multi-ply thread as it adds bulk and slightly overestimates the size. Embroidery thread is ideal.

✓ Great

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Thin Twine / Kite String

Works in a pinch if the twine is non-elastic and consistent in thickness. Avoid fluffy or textured twine as it compresses under finger pressure and gives inconsistent readings.

⚠️ Acceptable

🧤

Wool / Yarn / Elastic Thread

Do NOT use. Wool and yarn are elastic and compress under tension — they consistently give a measurement 1–2mm smaller than your actual finger circumference, causing you to order too small.

✗ Avoid

⚠️ Critical: Never use elastic, stretchy, or fluffy materials. Dental floss or a single strand of cotton thread gives the most accurate reading. When in doubt, substitute with the paper strip method — paper cannot stretch at all.

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How to Measure Ring Size With String — Step by Step

What you need: A piece of dental floss or non-elastic string (approx. 15 cm) · A fine-tip pen or marker · A ruler with millimetre markings · The ring size chart below (or the calculator)

Cut approximately 15 cm of string or dental floss

Cut a piece of dental floss or non-elastic string approximately 15 cm (6 inches) long. This gives you enough length to wrap around your finger, overlap, and still have enough to hold while marking. Dental floss is the ideal choice — it is thin, non-elastic, and consistent in width. Do not use elastic thread, wool, or yarn.

Wrap once around the base of the correct finger

Wrap the string once around the base of the specific finger you plan to wear the ring on. For most people this is the left-hand ring finger (for engagement and wedding rings) or the right-hand ring finger. Keep the string flat and smooth — not twisted or bunched. It should feel snug against your skin but not tight enough to cause discomfort or restrict blood flow. You should be able to slip your fingernail underneath it.

Check it passes over your knuckle

Before marking, gently slide the string loop upward toward your knuckle. The loop must pass over your knuckle without forcing — otherwise the ring will not fit on your finger regardless of how the base measurement looks. If your knuckle is noticeably wider, loosen the string slightly until it passes over comfortably, then re-snug it at the base. Your ring size should accommodate both the base and the knuckle.

Mark the exact overlap point with a pen

Hold the string firmly in position and use a pen or fine marker to mark precisely where the string overlaps itself — the exact point where one end meets the other. Press gently to make a clean, sharp mark. Remove the string carefully from your finger without stretching it. Do not pull the string tight as you remove it.

Measure from the end to the mark in millimetres

Lay the string flat on a ruler. Measure from one end of the string to the pen mark in millimetres (mm). Make sure the string is completely straight and not curved or bunched on the ruler. The measurement you read is your inner finger circumference in mm. Enter this number into the calculator below, or find it in the Inner Circumference (mm) column of the size chart to get your AU, US, EU, and Japan ring sizes instantly.

✅ Example: You measure 54 mm of string from end to mark. In the size chart below, 54.3 mm = AU Size N / US 7 / EU 54 — the most common women's ring size in Australia. If your measurement is between two sizes, always choose the larger size.

🔁 Measure 3 Times for Best Accuracy

①

Measure in the morning

Fingers are at their smallest in the morning when you wake up — typically before activity and warmth affect blood flow. Note this measurement.

②

Measure in the afternoon

Fingers are at their largest mid-to-late afternoon due to daily activity and warmth. This is the most important measurement for daily-wear rings. Note this measurement.

③

Average the results

Add your three measurements and divide by three. Use this average circumference to find your ring size. If the result falls between two sizes, round up to the larger size.

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Ring Size Calculator — String Measurement to Ring Size

Enter your string measurement to instantly find your AU, US, EU and Japan ring size

Your Ring Size

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Ring Size Chart — AU, US, EU & Japan

🇦🇺 AU / UK / NZ	🇺🇸 US / Canada	🇪🇺 EU / ISO	🇯🇵 Japan	Inner Diameter (mm)	String Length / Circ. (mm)	Typical Wearer
F	3	44.1	4	14.0 mm	44.1 mm	Child / Petite
F½	3.25	44.6	—	14.2 mm	44.6 mm	Child / Petite
G	3.5	45.3	6	14.4 mm	45.3 mm	Child / Petite
G½	3.75	45.9	—	14.6 mm	45.9 mm	Child / Petite
H	4	46.6	7	14.8 mm	46.6 mm	Small
H½	4.25	47.1	—	15.0 mm	47.1 mm	Small
I	4.5	47.8	8	15.2 mm	47.8 mm	Small Women
I½	4.75	48.4	—	15.4 mm	48.4 mm	Small Women
J	5	49.1	9	15.6 mm	49.1 mm	Small Women
J½	5.25	49.8	—	15.8 mm	49.8 mm	Small Women
K	5.5	50.4	10	16.0 mm	50.4 mm	Women
K½	5.75	51.1	—	16.2 mm	51.1 mm	Women
L	6	51.7	11	16.4 mm	51.7 mm	Popular ♀
L½	6.25	52.4	—	16.6 mm	52.4 mm	Popular ♀
M	6.5	53.0	12	16.8 mm	53.0 mm	Popular ♀
M½	6.75	53.7	—	17.0 mm	53.7 mm	Popular ♀
N ⭐	7	54.3	13	17.2 mm	54.3 mm	Most Common ♀
N½	7.25	55.0	—	17.4 mm	55.0 mm	Popular ♀
O	7.5	55.7	14	17.6 mm	55.7 mm	Popular ♀
O½	7.75	56.3	—	17.8 mm	56.3 mm	Popular ♀
P	8	57.0	15	18.0 mm	57.0 mm	Popular ♀
P½	8.25	57.6	—	18.2 mm	57.6 mm	Women / Men
Q	8.5	58.3	16	18.4 mm	58.3 mm	Women / Men
Q½	8.75	58.9	—	18.6 mm	58.9 mm	Men
R	9	59.6	18	18.8 mm	59.6 mm	Men
R½	9.25	60.2	—	19.0 mm	60.2 mm	Men
S	9.5	60.9	19	19.2 mm	60.9 mm	Men
S½	9.75	61.6	—	19.4 mm	61.6 mm	Men
T ⭐	10	62.2	20	19.6 mm	62.2 mm	Most Common ♂
T½	10.25	62.9	—	19.8 mm	62.9 mm	Men
U	10.5	63.5	21	20.0 mm	63.5 mm	Men
V	11	64.8	23	20.4 mm	64.8 mm	Large Men
W	11.5	66.2	24	20.8 mm	66.2 mm	Large Men
X	12	67.5	—	21.2 mm	67.5 mm	XL Men
Z	13	70.1	27	22.0 mm	70.1 mm	XL Men

⭐ AU N = Most common women's size — 54.3 mm string measurement

⭐ AU T = Most common men's size — 62.2 mm string measurement

🔼 Always round UP when between sizes

🇦🇺 AU = UK = NZ — identical letter sizing

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Convert String Measurement to Ring Size — Formulas

String Measurement Conversion Formulas

String Length (Circumference) → Ring Diameter

Diameter (mm) = String length (mm) ÷ 3.14159

Example: 54.3 mm ÷ 3.14159 = 17.3 mm diameter → AU Size N (women's average). Use this if you want to double-check using the diameter column of the chart.

Centimetres → Millimetres (if you measured in cm)

mm = cm × 10

Example: If your ruler shows 5.4 cm, that is 54 mm → match to the circumference column. Always convert to mm before using the chart — all ring size charts use millimetre values.

Inches → Millimetres (if you measured in inches)

mm = inches × 25.4

Example: 2.14 inches × 25.4 = 54.3 mm → AU Size N. Always convert to mm before looking up the chart to avoid confusion between measurement systems.

Quick Read: EU Size = String length in mm (no calculation needed)

EU ring size = inner circumference in mm = your string measurement

Example: String measures 54 mm → EU size 54 → AU Size N. EU sizing is the same number as your millimetre string measurement, which makes this the easiest conversion of all.

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String Method — Do's & Don'ts

✅ DO

>Use dental floss or a single strand of cotton thread >Wrap at the base of the finger where the ring will actually sit >Check the loop passes over your knuckle before marking >Keep the string flat and smooth — not twisted or bunched >Mark with a fine-tip pen for a precise mark >Lay the string completely straight on the ruler when measuring >Measure in millimetres — not centimetres or inches >Measure 3 times at different times of day and average >Round UP when between two sizes >Measure in the afternoon for daily-wear rings

✗ DON'T

>Use wool, yarn, or any elastic / stretchy material >Pull the string tight — it should be snug, not constricting >Let the string twist around the finger — keep it flat >Measure in the morning only — fingers are smallest then >Measure when fingers are cold, wet, or swollen >Forget to account for the knuckle >Measure the wrong finger or wrong hand >Let the string curve or kink when measuring on the ruler >Round down when between two sizes >Rely on a single measurement without repeating

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Expert Tips for the String Method

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Dental floss is your best friend — it is the single best material for the string method. It is non-elastic, available in every home, glides smoothly over the knuckle, and is thin enough that it doesn't add bulk to the measurement. Waxed or unwaxed dental floss both work equally well.

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Lay the string completely flat on the ruler — the most common mistake with the string method is letting the string curve or wave on the ruler. Lay it straight from one end. Even a 1mm reading error changes your ring size by one half-size, so precision here matters.

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Measure in the afternoon for daily-wear rings — fingers are 0.5 to 1 full ring size larger in the afternoon than in the morning due to warmth and blood flow. If the ring will be worn every day (wedding band, engagement ring), afternoon measurement gives the most comfortable long-term fit.

🌡️

Warm hands before measuring — cold fingers can be significantly smaller than warm fingers. Before measuring with string, wash your hands with warm water or spend a few minutes in a warm room. This ensures you don't size too small and end up with a ring you can't wear comfortably in summer.

🦴

Always check the knuckle — before marking your string, slide the loop toward your knuckle. The string must pass over comfortably. If the knuckle is noticeably wider, measure both the base and the knuckle. The ring must clear the knuckle — a ring stuck below the knuckle is a safety hazard.

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Wide band rings need half a size up — after measuring with string (which measures a theoretical zero-width band), add half a size if the ring band is 5mm or wider. A 6mm–8mm band has significantly more surface contact and will feel tighter than the string measurement predicts.

🔁

If results vary between measurements, choose the largest — when your three measurements give different results (e.g. 53 mm, 54 mm, 55 mm), use the largest measurement to determine your ring size. A ring that is slightly loose is comfortable and can be resized — a ring that is too tight is painful and risky to wear.

🏪

When in doubt, go to a jeweller — if your three string measurements give inconsistent results or you are buying an expensive ring, walk into any Australian jeweller for a free professional sizing. Stores like Michael Hill, Shiels, and Moi Moi use precision mandrel tools and size customers in under two minutes at no charge.

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Frequently Asked Questions

How do you measure ring size with string? ▾

Wrap a piece of non-elastic string or dental floss around the base of your finger. Mark where the string overlaps with a pen. Lay the string flat on a ruler and measure the length from one end to the mark in millimetres. That number is your inner finger circumference — match it to the circumference column in the size chart above or enter it into the calculator to find your AU, US, EU, and Japan ring sizes.

What type of string is best for measuring ring size? ▾

Dental floss is the best material — it is non-elastic, thin, and consistent. A single strand of cotton thread or embroidery thread also works well. The critical rule is that the material must be non-stretchy. Avoid wool, yarn, elastic thread, or anything fluffy. These materials compress under finger pressure and give a measurement 1–2mm smaller than your true finger circumference, causing you to order a ring that is too small.

My string measured 54 mm — what ring size is that? ▾

54 mm (inner circumference) corresponds to AU Size N / US 7 / EU 54 / Japan 13 — the most common women's ring size in Australia. The inner diameter is 17.2 mm. If your measurement is exactly 54 mm, you are right on the border between AU M½ (53.7 mm) and AU N (54.3 mm) — choose AU N as you should always round up when between sizes.

Is the string method accurate enough for buying a ring? ▾

The string method with dental floss or cotton thread is accurate enough for most ring purchases, especially when you measure three times and average the results. It is slightly less accurate than a professional mandrel sizing at a jeweller, mainly because the accuracy of the mark and how flat you hold the string on the ruler both affect the result. For expensive or custom rings (over $500), always verify with a free professional sizing at a jeweller before ordering.

What if my string measurement falls between two ring sizes? ▾

Always choose the larger size. A ring that is half a size too large is comfortable to wear and can be resized down by a jeweller for $50–$150 AUD. A ring that is too small is painful, may not pass over your knuckle, and is structurally harder (and more expensive) to size up. The only exception is if you have a wide knuckle and very narrow finger base — in that case a jeweller visit is recommended before purchasing.

Why does my string measurement keep giving different results? ▾

Variation between measurements is normal and happens for several reasons: (1) fingers change size throughout the day (morning vs afternoon), (2) temperature affects finger size — cold = smaller, warm = larger, (3) slight differences in how tightly you wrapped the string, and (4) how flat the string was when you read the ruler. Always take 3 measurements, average them, and round up. If variation is large (more than 3mm), visit a jeweller for a professional sizing.

Can I use string to measure ring size for someone else secretly? ▾

Yes — if the person is asleep, you can gently wrap string around their finger, mark it, and measure it without waking them. However, the most reliable secret sizing method is to borrow a ring they already wear on the correct finger and take it to a jeweller for measurement. The jeweller reads the inner diameter in seconds. If you can't borrow a ring, measuring while they sleep with dental floss works as a backup.

How do I convert a string measurement in cm to a ring size? ▾

Multiply your centimetre measurement by 10 to convert to millimetres. For example, 5.4 cm × 10 = 54 mm → AU Size N / US 7. Then match the millimetre value to the Inner Circumference (mm) column of the size chart above. Always convert to mm before looking up the chart, as all international ring size charts use millimetre values.

Should I measure at the base of the finger or the knuckle? ▾

Measure at the base of the finger (where the ring will actually sit) but verify it passes over the knuckle. If the knuckle is wider than the base by 2mm or more, you may need to size the ring for the knuckle rather than the base to ensure the ring can be put on and taken off safely. In this case measure both, and choose a size between the two readings — or ask a jeweller for a comfort-fit profile ring, which is designed to accommodate this difference.