Can I measure my ring size without a ring sizer?

Yes. If you have a ring that fits well, matching its inner diameter to the on-screen circle is the most accurate method. If you don’t, wrap a strip of paper about 5 mm wide around the base of your finger, mark it, and read the length (inner circumference) with the on-screen ruler. Either way, you first need to calibrate the screen to actual size with a card or coin.

How do sizes relate to inner circumference and diameter?

Japanese size (JIS standard) is the inner circumference in mm minus 40. For example, size 9 is 49 mm around with an inner diameter of about 15.6 mm, size 11 is 51 mm and about 16.2 mm, and size 13 is 53 mm and about 16.9 mm. Each size up adds about 1 mm to the circumference and about 0.32 mm to the diameter.

Screen sizes vary by device. Can it really measure correctly?

Not as is, which is why you calibrate first. Hold something of a fixed size, such as a credit card or transit IC card (85.6 mm wide) or a 1 yen coin (20.0 mm in diameter), to the screen and match the displayed frame exactly, and the tool learns how many pixels make 1 mm on that screen. The circles and rulers after that are shown at actual size using that value.

What Japanese sizes do US and UK sizes correspond to?

As a guide, US 5 ≈ JP 9, US 6 ≈ JP 11–12, US 7 ≈ JP 14, and US 8 ≈ JP 17. UK sizes are letters: J ≈ JP 9, L ≈ JP 11–12, and N ≈ JP 14. For EU (ISO), the inner circumference in mm is the size itself, so EU 52 is JP 12. You can see the full list in the chart at the bottom of the page.

Should I change sizes for a wide ring?

The wider the band, the more of it touches your finger, so it feels tighter at the same size. As a guide, going up 0.5 size for 4–6 mm bands and 1 size for 6 mm or more makes it easier to get a good fit. In this tool, entering the band width updates the recommended size.

How can I secretly find out my partner’s size for a surprise engagement ring?

An easy way is to borrow a ring they usually wear, place it on the on-screen circle, and measure its inner diameter. However, the size depends on which finger they wear it on (the middle finger is generally thicker than the ring finger). The left and right hands can also differ, so choose a ring worn on the same finger of the same hand.

Does the time of day affect the result?

Yes. Fingers are thinner in the morning and on cold days, and thicker from swelling in the evening, on hot days, or after drinking alcohol. The difference can be about 0.5–1 size, so measure several times and go with the thicker reading to avoid a ring that’s too tight or won’t come off.

Measure Ring Size on Your Screen | Find Your Size from a Ring or String (US, UK, EU Conversion)

A tool to measure ring size on a phone or computer screen, no ring sizer needed. First you hold a credit card or a Japanese 1, 10, 100, or 500 yen coin to the screen to set “1 mm on this screen”, so differences in screen size between devices don’t matter. Measure in two ways: place a well-fitting ring on the on-screen circle and match its inner edge, or read the length of paper or string wrapped around your finger with the on-screen ruler. It shows inner circumference, inner diameter, Japanese size (JIS), US, UK, and EU (ISO) at once. It also suggests a size to buy based on band width (wider feels tighter), knuckle size, and the time of day you measured.

First, calibrate your screen to actual size

Screen sizes differ by device, so hold a card or coin to the screen to set “1 mm on this screen”.

Place a well-fitting ring on the on-screen circle and resize until the red line overlaps the ring’s inner edge. The key is to match the inside, not the outside.

Inner diameter 16.50 mm

RESULT

Japan (JIS)

12 JP

Exact: 11.8

Circumference / diameter

51.8mm

⌀ 16.5mm

US / UK

US 6

UK L

EU / ISO

Circumference in mm

You haven’t calibrated your screen yet, so the circle and ruler sizes aren’t accurate. Calibrate with “Calibrate to actual size” above.

Choosing for the ring you’ll buy

Band width: 3 mm

Thick knucklesMeasured in the morning, in winter, or with cold handsMeasured with string or paper

Recommended size: JP 12

For a thin ring around 3 mm wide, the measured size usually fits as is.

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Ring size chart (Japanese size, circumference, diameter, international sizes)

Press a row to show results for that size. US and UK sizes may differ by about 0.25–0.5 depending on the brand.

JP size	Circumference	Diameter	US	UK	EU
JP 1	41mm	13.1mm	1¾	C½	41
JP 2	42mm	13.4mm	2¼	D½	42
JP 3	43mm	13.7mm	2½	E	43
JP 4	44mm	14.0mm	3	F	44
JP 5	45mm	14.3mm	3¼	G	45
JP 6	46mm	14.6mm	3¾	G½	46
JP 7	47mm	15.0mm	4	H½	47
JP 8	48mm	15.3mm	4½	I	48
JP 9	49mm	15.6mm	5	J	49
JP 10	50mm	15.9mm	5¼	K	50
JP 11	51mm	16.2mm	5¾	K½	51
JP 12	52mm	16.6mm	6	L½	52
JP 13	53mm	16.9mm	6½	M	53
JP 14	54mm	17.2mm	6¾	N	54
JP 15	55mm	17.5mm	7¼	O	55
JP 16	56mm	17.8mm	7½	O½	56
JP 17	57mm	18.1mm	8	P½	57
JP 18	58mm	18.5mm	8½	Q	58
JP 19	59mm	18.8mm	8¾	R	59
JP 20	60mm	19.1mm	9¼	S	60
JP 21	61mm	19.4mm	9½	S½	61
JP 22	62mm	19.7mm	10	T½	62
JP 23	63mm	20.1mm	10¼	U	63
JP 24	64mm	20.4mm	10¾	V	64
JP 25	65mm	20.7mm	11¼	W	65
JP 26	66mm	21.0mm	11½	W½	66
JP 27	67mm	21.3mm	12	X½	67
JP 28	68mm	21.6mm	12¼	Y	68
JP 29	69mm	22.0mm	12¾	Z	69
JP 30	70mm	22.3mm	13	Z+	70

ABOUT

About Measure Ring Size on Your Screen | Find Your Size from a Ring or String (US, UK, EU Conversion)

The ring size measurer lets you find your ring size on a phone or computer screen, even without a ring sizer (a set of rings for measuring size). Screen sizes differ by device, so “1 cm on screen” isn’t really 1 cm as is. That’s why you first calibrate to actual size by holding something with a fixed size, such as a credit card (85.6 mm wide) or a 1 yen coin (20.0 mm in diameter), to the screen. Then place a well-fitting ring on the on-screen circle and match its inner edge, or read the length of paper or string wrapped around your finger with the on-screen ruler, and it shows the inner circumference, inner diameter, Japanese size (JIS), US, UK, and EU (ISO) sizes at once. Japanese size is “inner circumference (mm) − 40”, so size 9 is 49 mm around with an inner diameter of about 15.6 mm. Wider bands feel tighter at the same size, so it also suggests a size to buy based on band width, knuckle size, and the time of day you measured.

How to use Measure Ring Size on Your Screen | Find Your Size from a Ring or String (US, UK, EU Conversion)

1In “Calibrate to actual size”, hold a card or coin to the screen, resize until the frame or circle overlaps exactly, and press “Use this size”
2If you have a ring, choose “Place a ring on the screen” and resize until the red circle overlaps the ring’s inner edge
3If you don’t have a ring, choose “Measure with string or paper”, hold the marked paper you wrapped around your finger to the on-screen ruler, and move the red line to the mark
4Check the resulting Japanese size, inner circumference, inner diameter, US, UK, and EU sizes
5Enter the width of the ring you’re buying and whether your knuckles are thick to see the recommended size
6Copy the result or share it on X

Great for

Find your ring size before buying a ring online
Secretly borrow your partner’s ring and measure it for a surprise engagement ring or matching rings
Convert US or UK sizes of overseas brands to Japanese sizes
Decide what size to choose for a wide ring or fingers with thick knuckles
Find out the size of a ring at home when you can’t read the engraving
Use it as a ruler calibrated to actual size to measure small objects

Good to know

Because you measure on the screen, calibration determines accuracy. Adjust until the right edge of the card or the rim of the coin overlaps the frame line exactly. The calibration is saved in your browser for this device and screen size.
Changing the browser zoom (pinch or Ctrl + scroll wheel) shifts the size shown on screen. Use it at 100%, and recalibrate if you change the zoom.
When placing a ring, match the inner edge, not the outer edge. A 0.3 mm difference in inner diameter is about 1 mm (one Japanese size) in circumference.
String and paper tend to read small because they stretch or are pulled tight, so a +0.5 size correction is applied from the start when measuring with string.
Fingers are thicker in the evening than in the morning and in summer than in winter, and can change by about one size. Measure several times and go with the larger reading so the ring is less likely to slip off.
US and UK conversions use a common formula and may differ by about 0.25–0.5 sizes from a given brand’s or country’s chart. Also check the size chart of the store you buy from.
No images are taken or sent. All calculations happen in your browser.

Questions this tool answers

Use Measure Ring Size on Your Screen | Find Your Size from a Ring or String (US, UK, EU Conversion) for searches like these:

I don’t have a ring sizer but want to measure my ring size
I want to hold a ring to my phone screen to find its size
I want to get a ring size from the finger circumference I measured with string or paper
I want to know the size from a ring’s inner diameter
I want to know what Japanese size a US ring size is
I want to know what size to choose for a wide ring
I want to secretly find out a ring size for an engagement ring
I want to show an actual-size ruler on my screen

FAQ

Can I measure my ring size without a ring sizer?: Yes. If you have a ring that fits well, matching its inner diameter to the on-screen circle is the most accurate method. If you don’t, wrap a strip of paper about 5 mm wide around the base of your finger, mark it, and read the length (inner circumference) with the on-screen ruler. Either way, you first need to calibrate the screen to actual size with a card or coin.
How do sizes relate to inner circumference and diameter?: Japanese size (JIS standard) is the inner circumference in mm minus 40. For example, size 9 is 49 mm around with an inner diameter of about 15.6 mm, size 11 is 51 mm and about 16.2 mm, and size 13 is 53 mm and about 16.9 mm. Each size up adds about 1 mm to the circumference and about 0.32 mm to the diameter.
Screen sizes vary by device. Can it really measure correctly?: Not as is, which is why you calibrate first. Hold something of a fixed size, such as a credit card or transit IC card (85.6 mm wide) or a 1 yen coin (20.0 mm in diameter), to the screen and match the displayed frame exactly, and the tool learns how many pixels make 1 mm on that screen. The circles and rulers after that are shown at actual size using that value.
What Japanese sizes do US and UK sizes correspond to?: As a guide, US 5 ≈ JP 9, US 6 ≈ JP 11–12, US 7 ≈ JP 14, and US 8 ≈ JP 17. UK sizes are letters: J ≈ JP 9, L ≈ JP 11–12, and N ≈ JP 14. For EU (ISO), the inner circumference in mm is the size itself, so EU 52 is JP 12. You can see the full list in the chart at the bottom of the page.
Should I change sizes for a wide ring?: The wider the band, the more of it touches your finger, so it feels tighter at the same size. As a guide, going up 0.5 size for 4–6 mm bands and 1 size for 6 mm or more makes it easier to get a good fit. In this tool, entering the band width updates the recommended size.
How can I secretly find out my partner’s size for a surprise engagement ring?: An easy way is to borrow a ring they usually wear, place it on the on-screen circle, and measure its inner diameter. However, the size depends on which finger they wear it on (the middle finger is generally thicker than the ring finger). The left and right hands can also differ, so choose a ring worn on the same finger of the same hand.
Does the time of day affect the result?: Yes. Fingers are thinner in the morning and on cold days, and thicker from swelling in the evening, on hot days, or after drinking alcohol. The difference can be about 0.5–1 size, so measure several times and go with the thicker reading to avoid a ring that’s too tight or won’t come off.

Special Thanks

SOLO GUILD | サービス作るAIエンジニア

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