Which Finger to Measure for Ring Size (and Why)

Why each finger needs its own size

The Finger Guide puts numbers to what's obvious once you compare fingers side by side: tap any finger on the hand diagram and it shows average sizes and typical inside diameter for that one. The thumb runs 2 to 3 US sizes above the ring finger; the pinky drops 3 to 4 sizes below it.

Average sizes per finger, from the app's Finger Guide
Finger	Male avg.	Female avg.	Diameter
Ring finger	US 10 – 11	US 6 – 7	16.5 – 18.5 mm
Index	US 10.5 – 12	US 6.5 – 8	17.0 – 19.5 mm
Middle	US 11 – 12.5	US 7 – 8.5	17.5 – 20.0 mm
Pinky	US 7 – 9	US 4 – 6	14.0 – 16.5 mm
Thumb	US 12 – 14	US 8 – 10	19.0 – 23.0 mm

Use these as a sanity check, not gospel. If your own number lands way outside the range for that finger, measure again before you trust it. Land inside the range and your actual measurement still wins over the average.

Which part of the finger do you measure?

Measure at the base, where the ring will actually sit, but don't ignore the knuckle. A ring has to pass over it to get on. When the knuckle is noticeably wider, a base-only measurement can give a ring that won't go on — check both spots and size to the larger one.

Are both ring fingers the same size?

Usually not the same. The Finger Guide puts the left-right gap at half to one full US size, with the dominant hand running a quarter to half a size bigger. Measure the actual hand the ring goes on — not whichever one's free when you reach for the app.

Ring size morning vs night, and other factors

The Factors That Affect Ring Size section lists what makes a finger drift hour to hour:

Time of day: smallest in the morning, largest in the evening, a difference of a quarter to half a US size.
Temperature: cold shrinks fingers and heat swells them.
Hydration and salt: salty food causes water retention and swelling.
Exercise: wait 30 minutes after activity before measuring.
Altitude and travel: wait until you are acclimatised.

Does ring width affect ring size?

It does. A wide band grips more of the finger and feels tighter at the same nominal size than a thin one does. Go up half a size on anything wider than 6 mm, per the Finger Guide — that recommendation matches what jewelers tell you anyway.

Measuring the right finger with the app

Calibrate the screen once in Calibration.
Open Finger Guide and tap the finger you want, to see its typical range.
Open Finger Sizer, place that finger on the screen and widen the bars until they touch its sides at the base.
Tap Save Measurement. With Premium you can also record which finger it was in the measurement details.
Repeat on another day, ideally in the evening, and compare.

Questions and answers

Which finger is the thumb ring size compared to the ring finger?

2 to 3 US sizes bigger, per the Finger Guide. Thumb joints move around a lot too, so give the knuckle extra room to clear comfortably.

Should I measure my ring finger on the left or right hand?

Whichever hand actually gets the ring. They're rarely identical — expect half to one size apart.

How many times should I measure?

2 to 3 times, on different days, is what the Finger Guide recommends. One measurement might just catch you on a cold or swollen day.

How to measure your ring size at home with your phone · Ring Sizer

Which finger to measure for your ring size