How to Measure Ring Size with String

How to Measure Ring Size with String – UK Guide 2026

Complete step-by-step UK guide to measuring ring size using string, thread, or dental floss. Includes the standard string method, dental floss method, mistakes to avoid, and a full UK ring size chart from A to Z+2 in mm for 2026

🇬🇧 UK Ring Sizes A–Z+2 🧵 String Method 🦷 Dental Floss Method 🪡 Thread Method 📏 Measure in MM 🆓 100% Free ✅ 2026 Updated

How to Measure Ring Size with String – Quick Summary

Take a piece of non-stretchy cotton string (or dental floss — but not stretchy thread). Wrap it snugly around the base of the finger you'll wear the ring on. Mark the point where it overlaps with a pen. Lay flat and measure from the end to the mark in millimetres (mm) with a ruler. That number is your finger circumference — look it up in the UK ring size chart below to find your UK letter size.

🧵 String, pen & mm ruler ⏱️ Under 3 minutes 🆓 Completely free 📏 Accurate ±0.5–1mm

🧵 Items Needed
String · Pen · Ruler

±1mm

🎯 Accuracy of
String Method

3×

🔁 Measure This
Many Times

Evening

🌙 Best Time of Day
to Measure

ℹ️

How to Measure Ring Size with String – Overview 2026

The string method is one of the most widely used free at-home ring sizing techniques. It works identically to the paper strip method — wrap, mark, measure in mm, look up UK letter — but uses cotton string, thread or dental floss instead of paper. The key rule is to always use non-stretchy string: cotton thread, thin twine, or waxed dental floss. Avoid wool, elastic, or any stretchy thread, as these expand when wrapped and give a reading that is too small. Measure in the evening at room temperature and always repeat at least 3 times for accuracy.

🛒 What You Need to Measure Ring Size with String

3 household items — all you need for the string ring sizing method

🧵

Non-Stretchy String

Cotton thread, thin twine or waxed dental floss. Must not stretch.

✏️

Fine-Tip Pen

Ballpoint pen or fine marker for a precise overlap mark.

📏

MM Ruler

Ruler with clear millimetre markings — 15–30 cm length ideal.

✂️

Scissors (Optional)

To cut string to a workable length (~15 cm). Optional if snipping with nails.

🧵 Types of String You Can Use – Ranked

🦷

Dental Floss (Waxed)

Waxed dental floss is one of the best string options — it is non-stretchy, very thin for a precise mark, lies flat on a ruler, and is found in virtually every home. Use plain waxed floss, not mint tape or stretchy ribbon floss.

🧵

Cotton Sewing Thread

Standard cotton sewing thread from a sewing kit is ideal — thin, non-stretchy and holds its shape flat. Use a double strand if a single thread is too fine to mark clearly. Avoid polyester or elasticated thread.

🪡

Thin Cotton Twine

Thin household twine or packaging string works well. Choose the thinnest available to minimise width error. Ensure it is cotton-based and non-stretchy. Slightly less precise than thread or floss due to thickness.

🍀

Embroidery Thread

Cotton embroidery thread is a good alternative — typically 6-strand cotton with no stretch. Use a single or double strand. Available in most craft or sewing kits. Avoid synthetic embroidery threads which may have slight stretch.

⚠️

Avoid: Wool or Yarn

Wool, knitting yarn and most synthetic yarn are elastic — they stretch when wrapped around the finger, giving a reading that is smaller than your actual finger circumference. This will result in ordering a ring that is too small.

❌

Avoid: Elastic / Ribbon

Elastic thread, ribbon, and stretchy fabric strips all expand under tension and compress the finger slightly, both distorting the reading significantly. Never use any material with visible elasticity for ring sizing.

🧮 String Ring Size Calculator – UK 2026

Enter your string measurement to find your UK ring size instantly

Your UK Ring Size

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📋 Step-by-Step: How to Measure Ring Size with String

Cut approximately 15 cm of non-stretchy string or dental floss

Cut or pull off a length of about 15 cm of non-stretchy cotton string or waxed dental floss. This gives enough length to wrap around any finger with plenty of overlap for an easy, accurate mark. Avoid using stretchy materials such as wool, elastic thread, or ribbon — these give an inaccurately small reading.

Warm your hands to room temperature before measuring

Cold fingers are up to one full UK ring size smaller than warm fingers. Run hands under lukewarm water or rub them together for 30 seconds before measuring. Measure in the evening at room temperature for best results — fingers are at their largest then due to warmth and daily circulation.

Wrap the string snugly around the BASE of the correct finger

Wrap the string around the base of the finger you will wear the ring on — just above where the finger joins the palm. The string should be snug but not tight: you should be able to slide it very slightly without it cutting into the skin. If you can see the string making an indentation, it is too tight and will give an inaccurately small reading.

Mark the overlap point with a fine pen

While holding the string in position around the finger, use a fine-tip pen or sharp pencil to mark the string at the exact point where it crosses over to complete the loop. Make the mark as fine and precise as possible. A thick smudged mark introduces an error of 0.5–1 mm — significant enough to affect the result by a full UK half-size.

Remove, straighten, and lay flat on a hard surface

Carefully remove the string from the finger without stretching it. Lay it flat on a hard, smooth surface — a table, book, or desk. Make sure the string lies in a perfectly straight line without any twists, loops or curves. Any bow or curl in the string will cause the ruler reading to be shorter than the actual circumference.

Measure from the cut end to your mark in millimetres

Place the zero end of your mm ruler at the very end (cut end) of the string. Read the measurement in millimetres (mm) at your pen mark — reading to the nearest 0.5 mm for maximum accuracy. This value is your finger circumference in mm — the key number for finding your UK ring size in the chart below.

Measure at least 3 times and take the average

Remove and re-wrap the string from scratch at least 2 more times. Record all three readings and divide the total by 3 to get the average circumference in mm. Three averaged measurements remove single-reading errors caused by slight variations in how tightly the string sits each time.

Look up your UK ring size in the chart below

Find your average mm reading in the Circ. (MM) column of the UK ring size chart in the next section. The UK letter in the first column is your ring size. If your measurement falls between two rows, always choose the larger UK letter size for a comfortable fit.

🔣 Converting Your String Measurement

MM (String) → UK Ring Size

Look up in Circ. (MM) column in chart below

Example: String measures 53.1 mm → UK Size N (women's popular size)

CM (String) → MM

MM = CM × 10

Example: String measures 5.31 cm × 10 = 53.1 mm → UK N

MM Circumference → MM Diameter

Diameter = Circumference ÷ π (3.14159)

Example: 61.4 mm ÷ 3.14159 = 19.56 mm diameter = UK T (men's most common)

Women's Most Common (UK M)

String should measure ~51.9 mm

= 5.19 cm = 16.5 mm inner diameter = US 6.5 = EU 52

📋 UK Ring Size Chart – String MM Reference 2026

UK Size	Circ. (MM) — String	Diam. (MM)	Circ. (CM)	🇺🇸 US	🇪🇺 EU	Best For
F	43.7 mm	13.9 mm	4.37 cm	3	44	XS Women
G	44.9 mm	14.3 mm	4.49 cm	3.5	45	Small Women
H	46.2 mm	14.7 mm	4.62 cm	4	46	Small Women
I	47.1 mm	15.0 mm	4.71 cm	4.5	47	Small Women
J	48.0 mm	15.3 mm	4.80 cm	5	48	Women
J½	48.7 mm	15.5 mm	4.87 cm	5.25	49	Women
K	49.3 mm	15.7 mm	4.93 cm	5.5	49	Women
K½	49.9 mm	15.9 mm	4.99 cm	5.75	50	Women
L ⭐	50.6 mm	16.1 mm	5.06 cm	6	51	Women Popular
L½	51.2 mm	16.3 mm	5.12 cm	6.25	51	Women Popular
M ⭐	51.9 mm	16.5 mm	5.19 cm	6.5	52	Most Common ⭐
M½	52.5 mm	16.7 mm	5.25 cm	6.75	53	Women Popular
N ⭐	53.1 mm	16.9 mm	5.31 cm	7	53	Most Common ⭐
N½	53.8 mm	17.1 mm	5.38 cm	7.25	54	Women
O	54.4 mm	17.3 mm	5.44 cm	7.5	54	Unisex
O½	55.0 mm	17.5 mm	5.50 cm	7.75	55	Unisex
P	55.9 mm	17.8 mm	5.59 cm	8	56	Unisex
Q	57.2 mm	18.2 mm	5.72 cm	8.5	57	Slim Men
R	58.5 mm	18.6 mm	5.85 cm	9	59	Men
S	59.7 mm	19.0 mm	5.97 cm	9.5	60	Men
T ⭐	61.4 mm	19.56 mm	6.14 cm	10	61	Men Most Common ⭐
T½	62.1 mm	19.76 mm	6.21 cm	10.25	62	Men Popular
U ⭐	62.7 mm	19.96 mm	6.27 cm	10.5	63	Men Popular
V ⭐	64.0 mm	20.37 mm	6.40 cm	11	64	Men Popular
W	65.3 mm	20.78 mm	6.53 cm	11.5	65	Men
X	66.6 mm	21.18 mm	6.66 cm	12	67	Large Men
Y	67.8 mm	21.59 mm	6.78 cm	12.5	68	Large Men
Z	69.1 mm	21.99 mm	6.91 cm	13	69	XL Men
Z+1	69.7 mm	22.20 mm	6.97 cm	13.5	70	XL / Custom
Z+2	72.3 mm	23.01 mm	7.23 cm	14	72	Custom

⭐ String reads ~51.9 mm = UK M (women's most common)

⭐ String reads ~61.4 mm = UK T (men's most common)

📏 Between two sizes? Always choose the larger UK letter

⚠️ 5 Common Mistakes When Measuring Ring Size with String

1. Using stretchy string or wool — elastic and wool expand when wrapped around the finger, giving a reading smaller than your actual circumference. Always use non-stretchy cotton thread, twine, or waxed dental floss.

2. Pulling the string too tight — the string should be snug, not constricting. If it leaves an impression on the skin, loosen slightly and re-measure.

3. Letting the string twist or curl when measuring — always straighten the string fully on a flat surface before measuring. A twisted string reads shorter than its actual length.

4. Measuring in the morning or in cold conditions — fingers are significantly smaller in cold weather and first thing in the morning. Always measure in the evening at room temperature for the most accurate result.

5. Measuring only once — one reading can be off by 1–2 mm. Measure at least 3 times, take the average, and if readings vary by more than 1 mm, rest your hand for 5 minutes before re-measuring.

💡 Pro Tips for the String Ring Sizing Method

🦷 Waxed dental floss is your best option. It is thinner than most string, non-stretchy, lies perfectly flat, and can be marked cleanly with a fine pen. Available in every bathroom cabinet. Use plain waxed floss — not mint tape or stretchy ribbon floss.
📏 Always measure in mm, not cm. UK ring half-sizes are only 0.6–1.3 mm apart in circumference. Reading in cm only gives you 1 mm precision at best — you need mm precision to reliably identify your correct UK half-size.
🌙 Measure in the evening at room temperature. Fingers are at their largest daily size in the evening when warm. A morning measurement on the same finger can read a full UK letter size smaller. Avoid measuring immediately after cold exposure or vigorous exercise.
✋ Measure the exact hand and finger the ring will be worn on. Your dominant hand is typically 0.5–1 UK size larger than your non-dominant hand. Never measure one hand and assume the other is the same size.
📐 Check over your knuckle if it is noticeably wider. Wrap the string at the knuckle as well as the finger base and note both readings. If your knuckle is significantly wider, size to the knuckle measurement so the ring can slide on. A jeweller can advise on comfort-fit bands for large knuckle-to-base differences.
💍 Add half to one UK size for wide bands (6 mm+). Wide bands press against more skin than slim rings, making the same nominal UK size fit tighter. If purchasing a band 6 mm or wider, order approximately 0.5–1 full UK letter size larger than your string measurement.
⬆️ When between two UK sizes, always go larger. A slightly loose ring is comfortable and can be resized down at any UK jeweller for a small fee. A ring that is too tight can be uncomfortable and more expensive to resize upward.

🔗 Related UK Ring Size Guides

📌 More Pages on This Site

📋 Full UK Ring Size Chart A–Z+2 📜 How to Measure Ring Size with Paper 📐 How to Measure Ring Diameter 🏆 Best Way to Measure Ring Size 🔄 UK to US Ring Size Conversion

🌐 Trusted UK Jeweller Resources

📐 Oliver Bonas – How to Measure Ring Size 📐 Blue Nile – Ring Size Guide 📐 Daniel Wellington – Ring Size Guide

❓ How to Measure Ring Size with String – FAQs

How do I measure ring size with string? ▼

Cut approximately 15 cm of non-stretchy cotton string or waxed dental floss. Wrap it snugly around the base of the finger you plan to wear the ring on. Mark the point where the string overlaps with a fine pen. Remove, straighten and lay flat on a hard surface. Measure from the end to your mark in millimetres with a ruler. Look up the mm value in the Circ. (MM) column of the UK ring size chart above to find your UK letter size. Repeat 3 times and take the average.

Can I use dental floss instead of string to measure ring size? ▼

Yes — waxed dental floss is one of the best materials for the string ring sizing method. It is non-stretchy, very thin (giving a precise mark), lies completely flat on a ruler, and is found in most homes. Use plain waxed floss only. Avoid mint tape (too wide and soft), stretchy ribbon floss, or satin floss, as these may distort the measurement slightly. The technique is identical to the cotton string method: wrap, mark, measure in mm, look up UK size.

How accurate is the string method for UK ring sizing? ▼

The string method is accurate to approximately ±0.5–1 mm when performed correctly with non-stretchy cotton thread or waxed dental floss. The paper strip method is slightly more accurate (±0.5 mm) because paper cannot twist when laid flat. For the string method, the main sources of error are string stretch (use non-stretchy material only), string twisting when measuring, and a thick pen mark. Measuring 3 times and averaging removes most single-reading errors. For engagement rings or rings over £100, follow up with a professional jeweller sizing.

What type of string should I NOT use to measure ring size? ▼

Never use wool, knitting yarn, elastic thread, ribbon, satin cord, or any stretchy material. These expand under tension when wrapped around the finger, giving a reading that is smaller than your actual finger circumference — which results in ordering a ring that is too small. The rule is simple: only use materials with zero stretch, such as cotton thread, thin twine, or waxed dental floss.

My string measurement falls between two UK ring sizes — which do I choose? ▼

Always choose the larger UK ring size. A ring that is very slightly loose is comfortable and can be resized down at any UK jeweller for approximately £15–£40. A ring that is too tight is uncomfortable, may restrict circulation, and is more expensive to resize upward. If you consistently fall between two sizes after averaging 3 measurements, measure again in the evening at room temperature and confirm you are wrapping at the finger base, not the knuckle.

Is the string method or paper method more accurate for ring sizing? ▼

The paper strip method is marginally more accurate (±0.5 mm) than the string method (±0.5–1 mm) because paper lies perfectly flat on a ruler without any risk of twisting or curling, making the mm reading more precise. String can twist slightly when laid flat, introducing a small additional error. For most fashion ring purchases, both methods are sufficiently accurate. For engagement rings or any high-value purchase, a professional jeweller sizing is always recommended regardless of which at-home method you use.