G-Shock GA-B2100

Ref. GA-B2100-1A

Case diameter: 45.4 mm; Manufacturer spec
Lug-to-lug: 48.5 mm; Manufacturer spec
Thickness: 11.9 mm; Manufacturer spec
Lug width: —; Not published

Retail price $165 (US, Oct 2026)

Your wristIdeal fit

Wrist flat: 55.1 mmLug-to-lug: 48.5 mm

How the G-Shock GA-B2100 wears

Its lugs add only 3.1 mm to the 45.4 mm case, against 7.1 mm typical across the almanac, so it wears smaller than its diameter suggests.

On our fit model it sits best on wrists from 6.75" to 8" (17.1–20.3 cm); below 6.75" the lugs start to reach the edge of the wrist.

At 11.9 mm thick it is slimmer than 60% of the 10 other digital watches we've measured, so it slides under a cuff more easily than most.

Will the G-Shock GA-B2100 fit your wrist?

With a 48.5 mm lug-to-lug, here is how it wears across common wrist sizes. We estimate the flat top of each wrist from its circumference; measure yours for a closer answer in the fit finder.

Wrist	Flat width (est.)	Fit
6"	47.2 mm	Lugs overhang
6.5"	51.2 mm	Snug, lugs near the edge
7"	55.1 mm	Ideal fit
7.5"	59.1 mm	Ideal fit
8"	63 mm	Ideal fit

Specifications

Reference: GA-B2100-1A
Collection: G-Shock
Status: In production
Case material: carbon / resin
Crystal: mineral
Water resistance: 200 m
Bezel: resin (Carbon Core Guard)
Dial: black
Strap / bracelet: resin band
Weight: 52 g
Style: Digital, Sport

Movement

Caliber: Casio 5689
Type: solar
Accuracy: +/-15 s/month (without mobile link)

More G-Shock references

Watches that wear the same size

Other watches within 1.5 mm of its lug-to-lug.

Sources

casio.com/us/watches/gshock/product.GA-B2100-1A/