📐 Clinical Fit Protocol · Zero Guesswork

Smart Ring Size Calculator & MM Conversion Matrix

Convert finger circumference or inner diameter in millimeters into your exact US smart ring size (Sizes 6 through 13).

Quick Take (Bottom Line Up Front): To calculate your smart ring size, wrap a paper strip around your finger base and knuckle, mark the overlap in millimeters, and match the circumference against the US sizing scale. For optimal optical sensor contact with digital arteries, smart rings require a snug fit on the Index, Middle, or Ring finger. If between sizes, always select the larger size.

Finger Circumference in Millimeters (mm) Wrap a strip around knuckle & base; measure total length.

Inner Diameter of Existing Ring (mm) Measure straight across the inside edge of a well-fitting ring.

Target Finger

💡 Pro Sizing Tip: Fingers swell 0.3mm–0.5mm at night. Always test size in the evening at ambient room temperature.

Recommended US Ring Size

US 9

Inner Circumference: 59.5 mm · Inner Diameter: 18.9 mm

✓ Optimal arterial pulse telemetry on Index Finger

Official GridsGear Smart Ring Sizing Matrix

Standardized medical-grade dimensions for GridsGear Ring R1 (Aerospace Titanium Shell).

US Size	Inner Circumference (mm)	Inner Diameter (mm)	Best Anatomical Finger	Availability
Size 6	51.8 mm	16.5 mm	Ring / Index	✓ In Stock
Size 7	54.4 mm	17.3 mm	Index / Middle	✓ In Stock
Size 8	56.9 mm	18.1 mm	Index / Middle / Ring	✓ In Stock
Size 9	59.5 mm	18.9 mm	Index / Middle	✓ In Stock
Size 10	62.1 mm	19.8 mm	Index / Middle / Thumb	✓ In Stock
Size 11	64.6 mm	20.6 mm	Middle / Thumb	✓ In Stock
Size 12	67.2 mm	21.4 mm	Middle / Thumb	✓ In Stock
Size 13	69.7 mm	22.2 mm	Thumb / Middle	✓ In Stock

Frequently Asked Questions: Smart Ring Sizing

Are smart rings sized the same as standard jewelry rings?

Smart rings have inner sensor bumps (PPG optical domes and temperature sensors) that create a slightly firmer profile than flat jewelry bands. For this reason, we recommend choosing your size based on our dedicated smart ring millimeter chart or wearing our physical sizing kit for 24 hours.

Which finger is best for sleep tracking and HRV?

The index finger has the highest density of palmar digital arteries, delivering a pulse amplitude up to 3.8× stronger than other fingers. However, the middle and ring fingers offer identical clinical HRV accuracy when the ring is properly fitted.

What if my ring arrives and does not fit?

GridsGear offers a 7-day hassle-free replacement warranty across Pakistan. If your size is slightly loose or tight, our WhatsApp concierge arranges an exchange courier directly to your doorstep.