Model guide · Reviewed
G-SHOCK GA-2100 “CasiOak”: Size, Battery Life, Water Resistance & Specs
Short answer
The G-SHOCK GA-2100 is Casio's slim octagonal analog-digital watch, nicknamed the “CasiOak”, measuring 11.8 mm thick and weighing 51 g.
- Thickness
- 11.8 mm
- Weight
- 51 g (1.8 oz)
- Water resistance
- 200 m / 20 bar
- Power
- 3-year battery
Casio launched the GA-2100 in 2019 as a modern take on the octagonal bezel of the very first G-SHOCK, the DW-5000C. A carbon fiber–reinforced resin case (Carbon Core Guard) keeps it to 11.8 mm thick and 51 g while staying shock resistant and rated to 200 m. It runs about three years on two SR726W batteries, and its flat eight-sided bezel is why it became the most customized G-SHOCK: painted cases, metal bezels and moissanite bezels all start here.
GA-2100 specifications
Casio's specifications for the stock GA-2100-1A1. Custom builds can differ; see the notes below.
| Reference | GA-2100-1A1 |
|---|---|
| Module | 5611 |
| Display | Analog-digital |
| Shape | Octagonal |
| Case size (L × W × H) | 48.5 × 45.4 × 11.8 mm (1.91 × 1.79 × 0.46 in) |
| Weight | 51 g (1.8 oz) |
| Case | Carbon fiber–reinforced resin (Carbon Core Guard) |
| Band | Resin |
| Band fits wrists | 145–215 mm (5.7–8.5 in) |
| Water resistance | 200 m (660 ft, 20 bar) |
| Power | Battery: SR726W × 2, about 3 years |
| Tough Solar | No |
| Multi-Band 6 (atomic time) | No |
| Bluetooth | No |
| Light | Double LED (dial and LCD) |
| Launched | 2019 |
| Casio U.S. list price | $110 |
Features
- World time (31 time zones, 48 cities + UTC)
- 1/100-second stopwatch
- Countdown timer
- 5 daily alarms
- Neobrite luminous hands
- Mineral glass
- Carbon Core Guard structure
What is the G-SHOCK GA-2100?
The G-SHOCK GA-2100 is Casio's slim octagonal analog-digital watch, launched in 2019 and nicknamed the “CasiOak”. It pairs analog hands with a small LCD, uses module 5611 and is built on a carbon fiber–reinforced resin case.
Why is the GA-2100 called the CasiOak?
Fans call the GA-2100 the “CasiOak” because its octagonal bezel recalls far pricier luxury sports watches. It is a community nickname, not a Casio product name, and Casio itself traces the shape back to the original DW-5000C G-SHOCK.
How big is the GA-2100?
The GA-2100 measures 48.5 × 45.4 × 11.8 mm and weighs 51 g, according to Casio. That is about 1.9 × 1.8 × 0.46 inches and 1.8 oz, slim and light for a G-SHOCK, and its resin band fits wrists of roughly 145–215 mm (5.7–8.5 in).
Is the GA-2100 good for small wrists?
The GA-2100 is one of the better G-SHOCKs for small wrists because it is only 45.4 mm wide and 11.8 mm thick. Wrists around 6–6.5 in (15–16.5 cm) usually wear it well; for something smaller still, look at Baby-G or the slimmer GMA-S2100.
Can you swim with a GA-2100?
The stock GA-2100 is rated 200 m (660 ft, 20 bar) water resistant by Casio, so swimming and showering are fine. It is not an ISO-certified dive watch, and on a custom build painted or swapped parts can affect sealing, so confirm the specific piece with us before you swim.
How long does the GA-2100 battery last?
The GA-2100 runs about 3 years on two SR726W silver-oxide batteries, according to Casio's specification. It is not solar powered; the GA-B2100 is the solar version of the same octagonal design.
What module does the GA-2100 use?
The GA-2100 uses Casio module 5611, which is stamped on the case back. Casio's module 5611 manual covers setting the time, world time, the stopwatch, timer and alarms.
Does the GA-2100 have solar or Bluetooth?
No, the GA-2100 has neither Tough Solar charging nor Bluetooth. Casio's GA-B2100 adds both in a nearly identical 11.9 mm case, while the GA-2100 keeps a simple battery-powered quartz movement.
How much does a GA-2100 cost?
Casio's U.S. list price for the stock GA-2100-1A1 is $110, as recorded by G-Central, and retailers often discount it. Bezelwright currently lists 67 custom GA-2100 builds from $105, each with its own colorway or finish.
What changes on a custom GA-2100?
A custom GA-2100 changes the look of the watch, such as colorway, case and bezel finish or an aftermarket bezel, while the base model stays a GA-2100. Bezelwright is an independent customizer, not affiliated with Casio, and each listing states what is included.
Is the GA-2100 right for you?
The GA-2100 suits
- Anyone who wants a light, slim everyday G-SHOCK that slides under a shirt cuff.
- Smaller wrists: at 45.4 mm wide it wears smaller than most analog-digital G-SHOCKs.
- Customizers: the flat octagonal bezel is the easiest canvas for color, metal and moissanite.
Look elsewhere if
- Buyers who want solar charging or phone sync — the GA-B2100 adds both in the same shape.
- Divers who need an ISO-certified dive watch.
Custom GA-2100 builds: what changes
- Our GA-2100 builds change the look — colorways, painted or metal-finished cases and bezels — on the GA-2100 platform.
- Modifications can affect water resistance, so we confirm the rating of a specific piece before you swim with it.
- Moissanite bezels for the GA-2100 are sold separately and fit the GA-2100 case only (not the GM-2100 or GA-B2100 unless the listing says so).
Bezelwright is an independent customizer and is not affiliated with Casio. Specs above describe Casio's stock model.
Custom GA-2100 builds (67, from $105)
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Sources
Figures describe Casio's stock reference model. Independent references are used where Casio's own page could not be read directly, and cross-checked against Casio's published specs.
- Casio: GA-2100-1A specifications (official Casio, accessed October 25, 2026)
- Casio G-SHOCK (U.S.): GA2100: Slim & Tough Analog-Digital Watches (official Casio, accessed October 25, 2026)
- Casio: GA-2100K-1A specifications (battery, band size) (official Casio, accessed October 25, 2026)
- G-Central: G-SHOCK GA-2100 specifications (independent reference, accessed October 25, 2026)
- Casio G-SHOCK (UK): Are G-SHOCK watches waterproof or water resistant? (official Casio, accessed October 25, 2026)
- Casio (U.S.): GA-B2100-1A specifications (official Casio, accessed October 25, 2026)