Buying or commissioning a ring should feel exciting, not stressful. Yet the moment sizing comes up, many shoppers freeze—letters, numbers, diameters, half-sizes, US conversions—where do you even start? Take a breath; you only need two things for a spot-on fit: a simple measurement and a clear UK ring size chart. Everything else is optional.

This guide hands you both. You’ll see exactly how the UK’s letter system relates to millimetres around your finger, why a single millimetre can decide whether a ring spins or sticks, and which at-home tools give measurements a jeweller can trust. Printable templates, phone apps, quick conversion tables, even stealth methods for surprise proposals—all gathered here and road-tested by Hatton Garden goldsmiths. Read on, match your measurement to the chart, and step into the studio (or hit the checkout) knowing the band you choose will feel as perfect on day one as it does for every anniversary that follows.

Step 1 – Understand How UK Ring Sizing Works

UK jewellers label rings with letters, starting at A (tiny) and running beyond Z for larger fingers. Unlike the numbered US or EU scales, each jump of one UK letter equals roughly 1 mm of extra inside circumference, so precision is baked into the alphabet. Most women’s purchases land between I and P, men’s between P and Z, yet those are only trends—your own finger could sit anywhere. Steer clear of vague “Small/Medium/Large” tags used by fashion brands; fine jewellery needs a letter.

Letter Sizes, Diameters & Circumferences

The maths is simple: inside diameter × π = circumference. Here’s a snapshot for size M:

Men’s vs Women’s Sizing: Myths Debunked

Letters aren’t gendered. Charts marketed as “men’s” merely highlight bigger letters because broader hands order them more often. Always measure—guessing from gender averages is the fastest route to a resize.

Numbers to Letters & Half Sizes

A half size (e.g., L½) splits the 1 mm step, giving about 0.5 mm extra circumference. Jewellers achieve this by shaving or adding a sliver of metal. Opt for the half-step when the band is wider than 4 mm, features tension settings, or you sit bang between two letters.

Step 2 – Prepare the Right Measuring Tools at Home

Before you dash to a jeweller, raid the house. A sheet of A4, some scissors, string or a spare ring can all give a reading close enough for professional work.

Printable Ring Sizer (Paper Belt or Circle Chart)

• Accuracy: ★★★★☆
• Print at 100 %, cut out, and slide the paper belt through its slot. The size window shows your letter; cross-check by dropping an existing ring over the printed circles.

String or Paper Strip & Ruler

• Accuracy: ★★★☆☆
• Cut a ≤ 3 mm strip, wrap it snugly round the base of the finger, mark the overlap, then measure the length in millimetres. Convert with the chart.

Measuring an Existing Ring with Calipers/Ruler

• Accuracy: ★★★★★ with calipers; ★★★★☆ with ruler
• Measure the inner diameter only. Even a £5 plastic caliper reads to 0.1 mm and removes most guesswork.

Digital & Phone-App Methods

• Accuracy: ★★☆☆☆
• Apps overlay circles on your screen; drop a ring on top and match edges. Useful confirmation, but rely on another method first because screen scaling varies.

Step 3 – Measure an Existing Ring for a Loved One (Secret or Not)

Got access to a ring they already wear on the correct finger? Lucky you. Measuring that piece is quick, accurate and—if you play it cool—won’t blow the surprise proposal or birthday reveal.

Inner Diameter Method

1. Lay the ring on a millimetre ruler or caliper.
2. Read the widest inner edge only (ignore the metal thickness).
3. Note the measurement to 0.1 mm and match it to the diameter column of our UK ring size chart.

Circumference Method with Flexible Tape

• Thread a thin sewing tape around the inside of the ring.
• Mark where the tape meets, then flatten and measure the length in mm.
• Convert that figure using the circumference column.

Cross-Check Against a Printable Circle Chart

Drop the ring over the printed circles labelled A–Z. The right size is the one where the inner edge sits exactly on the line—no gap, no overlap. Always confirm with at least two of these methods for peace of mind.

Step 4 – Measure Your Finger Directly

No spare ring? No problem. Measuring the finger itself is just as reliable, provided you control the variables that make hands swell or shrink during the day. Work methodically, jot down every reading in millimetres, and always round up to the nearest half-size if you’re on the fence—resizing down is easier than adding metal later.

Timing & Temperature Best Practices

Hands are smallest in the morning and when cold, largest after exercise, heat or an evening tipple. Aim for mid-afternoon, normal body temperature, and hydrated. Take two readings a couple of hours apart; if they differ, use the larger one.

String/Paper Strip Walk-Through

1. Cut a strip ≤ 3 mm wide.
2. Wrap it around the finger base; mark the overlap.
3. Flatten and measure the length (mm).
4. Match it to the circumference column of the ring size chart.

Quick reference:

Adjustable Plastic Ring Sizer

Order a zip-tie style sizer for a couple of pounds online. Slide it on until snug, then read the letter in the window. Repeat twice; if readings vary, choose the larger. These tools are reusable, so keep one in the drawer for future gifts.

Professional In-Store Sizing

When the ring will cost more than about £500, or features an eternity or tension setting, pop into a jeweller for a ten-minute gauge check. Steel ring sticks and calibrated mandrels remove every last half-millimetre of doubt, and most shops (including ours) offer the service free.

Step 5 – Use the UK Ring Size Chart & Conversion Tables

You’ve got the millimetres; now match them to a letter. The master chart below converts every UK size from A through Z + 3 into the figures most people search for—inside diameter and circumference in millimetres, plus the nearest US and EU numbers. Because manufacturing tolerances round to the nearest tenth of a millimetre, treat the US/EU columns as guides, not gospel.

Complete A–Z UK Ring Size Chart

Bolded letters mark the sizes most often ordered (L–N for women, Q–T for men).

UK ↔ US & EU Quick-Look Conversion

Need a snapshot? Here are the ten sizes jewellers quote daily:

Ring Sizes in Millimetres & Centimetres

If someone asks, “What size ring is 7 cm?” simply divide: 70 mm of circumference corresponds to UK size W (US ≈ 11). Use the formula diameter × π = circumference to sanity-check any chart you find online.

Men’s & Women’s Charts Side-by-Side

Notice how the two spectrums overlap: the average woman’s range (I–P) sits squarely inside the men’s (P–Z). Letters stay unisex; your finger decides, not a marketing label.

Step 6 – Factor In Comfort Before Committing

A ring can be the right letter size on paper yet still pinch, spin or feel “off” once you start wearing it. Before you hit the buy button, weigh up the everyday realities that nudge a fit tighter or looser and tweak the size by half a letter if necessary.

Band Width, Profile & Metal Density

Wider bands cover more finger and need extra room. Anything over 6 mm typically calls for going up half a size, while domed “comfort-fit” interiors can stay true to size because the rounded edges glide over skin. Dense metals like platinum feel heavier but don’t change sizing maths.

Finger Swelling, Seasons & Daily Changes

Fingers enlarge in heat, after exercise or a salty lunch, and shrink in cold weather. Expect up to a ½-size swing across seasons; size for the largest comfortable measurement so the ring never becomes impossible to remove.

Knuckle vs Finger Base

If your knuckle is noticeably wider than the base, choose the smallest size that twists over with mild soap. Once on, the ring should sit snugly without spinning; a jeweller can add tiny sizing beads if it still swivels.

Engagement Ring & Wedding Band Stacking

Two or more bands worn together act like a single wide ring. Plan a combined width over 6 mm? Ordering the wedding band a quarter to half size larger avoids that tight “tourniquet” feel when both are stacked.

Step 7 – Troubleshoot & Answer Common Ring Size Questions

Still scratching your head? Below are the queries our Hatton Garden team hear every week—answered in plain English and cross-referenced to the steps you’ve just followed.

“How do I know my ring size in the UK?”

Start with what you have. If there’s an existing ring, jump to Step 3’s inner-diameter method; if not, follow Step 4’s finger-measurement guide. Cross-check against the A–Z chart and you’re done.

“Can my phone measure my ring size?”

Yes—apps that show on-screen circles get you in the right ballpark, but screen calibration varies. Treat the result as a second opinion, not the only measurement; confirm with paper, string or a jeweller.

“What size ring is 7 cm?”

Seventy millimetres of inside circumference converts to UK size W (US ≈ 11, EU ≈ 66). Use the master chart or the diameter × π formula if you’d like to verify.

“What if I’m Between Two Sizes?”

Rule of thumb: for narrow bands, size down; for wide or stacked bands, size up. Comfort-fit interiors can safely go smaller, while tension or eternity settings prefer the larger letter.

“How do I measure ring size at home without a printer?”

Skip the printout and use a 3 mm paper strip or non-stretch string plus a rigid ruler (Step 4). Mark, measure, convert—done. A reusable plastic zip-tie sizer is another cheap, printer-free option.

Step 8 – Resizing & Professional Help

Even with meticulous measuring, life happens—seasonal swelling, weight change, surprise stackable bands. Luckily, most quality rings can be resized by a competent bench jeweller.

When Resizing Is Straightforward vs Risky

Plain gold or platinum bands under 6 mm with no stone channel are a breeze: cut, add or remove metal, solder, polish. Eternity rings, tension settings and titanium / tungsten pieces are far trickier and sometimes impossible to alter without compromising integrity.

Typical UK Resizing Costs & Timeframes

Expect £30–£60 for a simple size change in 9 ct gold and £80–£120 for platinum. Most Hatton Garden workshops turn jobs around in two to five working days, including polishing and re-plating if required.

Information Your Jeweller Will Need

Have these details ready:

• Current ring size and target size
• Metal type and carat
• Presence of side stones or engraving
• Deadline (proposal date, wedding, etc.)

Lifetime Resize Policies to Look For

Many independent jewellers, including A Star Diamonds, offer one complimentary resize within 60 days—handy if jitters made you round the wrong way.

Secure the Perfect Fit Every Time

Getting ring size right isn’t luck—it’s a repeatable three-part recipe:

1. Measure with care (paper strip, caliper, or pro gauge).
2. Match that millimetre figure to the A–Z chart.
3. Adjust for real-life factors—band width, knuckle size and seasonal swelling.

Do that, and 99 % of fit headaches vanish before they start. If you’re still wavering between letters, go half a size larger; a snug band can always be eased, while a ring that’s too tight stays in the drawer.

When the piece carries real emotional or financial weight, add the final safeguard: an expert check. Drop into a trusted jeweller for a five-minute confirmation, or book a virtual sizing call if you’re miles away. At A Star Diamonds we throw in complimentary first resizing and lifetime clean-and-polish, so your ring keeps feeling—and looking—spot-on. Ready to make it official? Start the journey at A Star Diamonds.