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Casio Mudman 63.5mm Mens Watch Black
Ref. GDG-B100-1A5ER
Sits in Casio’s upper tier here — more premium than three quarters of the Casio watches we list, which start at £20.
Price range £20 to £919 across 152 Casio watches in stock.The Mudman name has always belonged to the Master of G line's mud-specialist — built to keep functioning when other watches would gum up and stop. This 2026 iteration marks the first time the model has carried a Memory-in-Pixel LCD, a display technology that becomes more legible the brighter the sun gets, inverting the usual problem with digital watches outdoors. What it has traded for that upgrade is Tough Solar and radio sync; timekeeping is handled through Bluetooth to the Casio app instead, and the battery is a standard coin cell rated at roughly two years. The Carbon Core Guard structure does the heaviest lifting here. Carbon fibre-reinforced resin gives the case genuine mud and impact resistance while keeping the whole thing to 66 grams — remarkable given how much watch this is physically. The extended bumper guards that push the lug-to-lug out to 63.6mm act as wrist-shaping wings rather than dead weight, distributing the case across the wrist rather than letting it sit proud of it. The red LED backlight is a considered choice: red light preserves night vision in a way white or green does not, which matters if you are moving in darkness and need to stay adapted to it. The mustard-yellow strap — a bio-based resin with a boot-tread pattern referencing the Mudman's mole mascot — is the one piece of levity in an otherwise tactical brief.
- Reference
- GDG-B100-1A5ER
- Brand
- Casio
- Collection
- G-Shock
- Case size
- 49.6mm
- Case thickness
- 16.2mm
- Case material
- Resin
- Case shape
- Octagonal
- Dial
- Black
- Crystal
- Mineral
- Movement
- Automatic
- Functions
- Stopwatch, Countdown timer, Alarm, Backlight, World time, Solar powered, Bluetooth, Step counter, GPS, Digital display
- Water resistance
- 200m
- Bracelet / strap
- Rubber strap
- Strap colour
- Yellow
- Clasp
- Buckle
- Lume
- Luminous
- Retailer
- Goldsmiths
Additional specifications
- Lug-to-lug
- 63.6mm
- Weight
- 66g
Learn more about Casio
Tadao Kashio founded Kashio Seisakujo in Tokyo in 1946 as a machine shop. The company's first success was a finger ring that held a cigarette, and its second was the 14-A of 1957 — the world's first all-electric compact calculator, which used solenoids rather than gears.
Casio entered watchmaking in 1974 with the Casiotron, a digital watch with an automatic calendar that knew the varying lengths of months. The company approached watches as an electronics manufacturer rather than a horological one, and that difference produced the G-Shock.
The G-Shock came from a single engineer, Kikuo Ibe, who broke a watch his father had given him and set out to build one that could not break. The specification was three tens: survive a ten-metre drop, ten bars of water pressure, and ten years of battery life. It took over two hundred prototypes, and the solution was suspending the module inside the case on a cushioned internal structure rather than mounting it rigidly. The DW-5000C shipped in 1983.
It became one of the most durable product designs in any category, adopted by militaries, emergency services, and skateboarders alike, and Casio has since added solar charging, radio and GPS timekeeping, Bluetooth, and full-metal and carbon variants.
Casio also produces the Edifice, Pro Trek, and Oceanus lines, and remains an independent Japanese public company.
- 1946
- Tadao Kashio founds the company in Tokyo.
- 1974
- The Casiotron is Casio's first digital watch.
- 1983
- The G-Shock DW-5000C survives Kikuo Ibe's three-tens brief.
- 1994
- The Frogman extends G-Shock to ISO dive certification.
Also in 7 collections
This watch appears in the Casio G-Shock range (91), Back in Stock (4,868), Automatic Watches (1,750), Watches 44mm and Over (802), Sports Watches (800), Dive Watches (572) and Automatic Watches Under £500 (336).
Manufacturer’s guarantee
What the specifications mean
A mechanical watch built to be worn hard and got wet.
Strengths
- 200m water resistance, rated for actual diving
- Luminous hands and markers for low light
- Second time zone for travelling
- One of Casio's more premium watches
Worth knowing
- 49.6mm is a large watch with real presence
- 16.2mm thick, so it will not disappear under a cuff
Casio Mudman alternatives
Watches from other brands at a similar price, style and size, so you can see what else your budget can buy.
| Specification | GDG-B100-1A5ER | RGS10082/03 | ME3082 |
|---|---|---|---|
| Price | £200 | £199 | £159 |
| Case size | 49.6mm | 49.5mm | 50mm |
| Water resistance | 200m | 50m | 50m |
| Movement | Automatic | Automatic | Automatic |
| Strap | Rubber strap | Leather strap | Leather strap |
| This watch |
|
|
Your new watch
Frequently asked questions, and things you should know about this watch
Can I swim with it?
Yes. At 200m it is rated for swimming, snorkelling and recreational diving.
Water resistance explainedWill the glass scratch?
It can, over time. Mineral glass handles daily wear but will pick up fine scratches that sapphire would not.
Sapphire, mineral and acrylic comparedDoes it need a battery?
No. It is automatic — the motion of your wrist winds it, and there is no cell to replace.
Quartz, automatic and solar comparedWill it fit my wrist?
Lug-to-lug is 63.6mm, which suits wrists from roughly 18.5cm (7¼ inches) upward.
Lug-to-lug decides fit more than case diameter does.
How to size a watch to your wristIs it a men's or women's watch?
Listed as men's.
Cheapest place to buy
Goldsmiths is the only UK retailer we track stocking this reference, so there is nothing to compare it against today.
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