3.50 Ct Emerald Cut Blue Sapphire and Lab-Grown Diamond Ring

Ordering a ring online shouldn't mean guessing. This guide covers the accurate ways to find your ring size at home, a full US size chart with millimeter measurements, and the fitting rules our NYC jewelers use every day. Every Zack & Elle ring is available in quarter sizes from 4 to 9 for a precise fit.

US Ring Size Chart (with millimeters)

Quarter sizes (4.25, 4.75, and so on) fall between the values above — we offer all of them, because a quarter size is often the difference between "fits" and "perfect."

Method 1: Measure a ring that already fits (most accurate at home)

1. Take a ring that fits the intended finger comfortably.
2. Measure the inside diameter edge-to-edge with a ruler, as precisely as you can (a caliper is even better).
3. Match it to the diameter column above. If you're between sizes, choose the quarter size in between.

Method 2: String or paper strip

1. Wrap a thin strip of paper or non-stretch string snugly around the base of the finger.
2. Mark where it overlaps, then measure the length in millimeters.
3. Match it to the circumference column above.

This method is less precise than measuring a ring — do it twice and use the average.

Fitting rules our jewelers actually use

• Measure at the end of the day. Fingers are smallest in the cold morning and largest in evening warmth — end-of-day is the honest size.
• The ring should resist slightly at the knuckle going on, and come off with a gentle pull. If it spins freely, it's too big.
• Wide bands fit tighter. For bands wider than ~6mm (full eternity styles), consider going up a quarter size.
• Dominant-hand fingers run about a quarter size larger.
• Don't size for the knuckle alone. If the knuckle is much larger than the finger base, split the difference.

Buying a surprise engagement ring?

• Borrow a ring she wears on that finger (left ring finger) and use Method 1.
• Ask a friend or family member who might know — it's the oldest trick because it works.
• When in doubt, size up. Sizing a ring down later is usually simpler than stretching it up.
• Still unsure? Call or text us at (646) 532-9004 — we help with surprise sizing every week, and we're a real workshop in NYC's Diamond District, so post-proposal adjustments are handled by the people who made the ring.

Ready when you are

Every engagement ring we make is available in sizes 4–9 including quarter sizes, in 14K gold, 18K gold, or platinum. Browse engagement rings, wedding bands, or best sellers — or call, text, or message us about sizing before you order.