Casio is a Japanese electronics company that entered the watch market in 1974 and has since become one of the world's largest watch producers by volume. The brand is best known for its G-Shock line of rugged digital watches, as well as its wide range of affordable digital and analog-digital timepieces. Casio watches carry model numbers and markings that follow systematic conventions, making identification relatively straightforward compared to some other brands. Understanding Casio's numbering system is helpful for collectors, particularly those interested in vintage digital watches and G-Shock models.
Casio Watch Markings & Identification Guide
Casio watches
Common Models
Casio G-Shock DW-5600Casio G-Shock GA-2100 (CasiOak)Casio A168WA (Vintage Digital)Casio F-91WCasio EdificeCasio Pro Trek
Serial Number Information
Casio watches typically feature a module number (also called a caliber number) on the case back, which is often a four-digit number identifying the electronic module inside the watch. This module number is commonly the most useful identifier, as it can be used to access Casio's online manual database to find the complete user manual and specifications for the watch. The module number is typically displayed prominently on the case back, often alongside or near the model reference.
The model reference number, which more specifically identifies the watch's design and variant, is also commonly found on the case back. For G-Shock watches, model numbers typically follow formats like 'DW-5600E' or 'GA-2100-1A1', where the letters indicate the series, the numbers identify the specific model, and the suffix indicates the color or variant. This model number can usually be looked up on Casio's website or in collector databases to identify the exact watch.
Casio watches may also feature a serial number for warranty and tracking purposes, though the serial number format and location can vary. Unlike some traditional watch brands, the serial number on a Casio watch is generally less useful for dating purposes, as the module number and model reference are typically more informative. For production date information, the date code stamped on the case back or printed on the battery compartment label can sometimes indicate the manufacture date.
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What to Check Next
Common Markings Found on Casio Watches
Model Number Stamp
An alphanumeric code stamped on the case back that identifies the specific watch model or product line. This number is essential for ordering replacement parts and identifying your watch's specifications.
Water Resistance Rating (Case Back)A marking indicating the watch's tested water resistance depth, typically shown in meters, feet, bar, or ATM. This rating describes laboratory test conditions, not actual diving depth recommendations.
Case Material MarkingAn engraving or stamp indicating the material the watch case is made from, such as stainless steel, titanium, or gold. This marking helps verify authenticity and informs care and maintenance decisions.
Crystal Press Back SymbolA small symbol on the case back indicating it should be opened with a crystal press tool rather than unscrewed. This marking guides watchmakers on the correct method for case back removal.
Japan Movement StampA case back marking indicating the watch uses a movement manufactured in Japan. This is commonly seen as "JAPAN MOVT" or "JAPAN MOVEMENT" and denotes the origin of the caliber inside.
Stainless Steel Back StampA marking reading "STAINLESS STEEL BACK" or "ST. STEEL BACK" indicating the case back material. This is commonly found on watches where only the back is stainless steel while the case body may be a different material.
Bezel Insert CodeA code identifying the specific bezel insert installed on a watch, typically relevant for dive watches and GMT models. This number is essential for sourcing correct replacement inserts.
Case Size IndicatorA marking indicating the watch case diameter or dimensions, typically in millimeters. This helps identify the watch model variant and determine strap compatibility.
WR 50M / 5 Bar MarkingA water resistance rating of 50 meters (5 bar/ATM), indicating the watch can handle everyday moisture like rain and hand washing. This rating is not suitable for swimming or submersion.
WR 100M / 10 Bar MarkingA water resistance rating of 100 meters (10 bar/ATM), generally considered suitable for swimming and recreational water activities. Not rated for scuba diving or high-impact water sports.
WR 200M / 20 Bar MarkingA water resistance rating of 200 meters (20 bar/ATM), suitable for serious water sports and recreational scuba diving. This is the standard entry-level rating for purpose-built dive watches.
Bar / ATM Pressure RatingA water resistance rating expressed in bar or ATM (atmospheres) instead of meters. One bar/ATM approximately equals 10 meters of water depth in testing pressure.
Japan Movt MarkingA case back marking indicating the watch uses a Japanese-manufactured movement. This is one of the most common markings found on affordable watches worldwide.
Made in Japan StampA marking indicating the watch was fully assembled in Japan, not just the movement. This designation is particularly valued on Seiko, Citizen, and Orient watches for the domestic Japanese market.
Kanji Case Back InscriptionJapanese characters (kanji or katakana) engraved or printed on the case back of watches sold in Japan. These inscriptions typically convey model names, material descriptions, or brand text written in Japanese.
JDM Model Reference CodeA model reference number specific to the Japanese domestic market that differs from the international version. JDM codes often follow unique formatting conventions, such as Seiko's alphanumeric SBDC or SARB prefixes.
PSC Diamond Safety MarkA small diamond-shaped symbol required on consumer products sold in Japan under the Product Safety of Consumer Products Act. On watches, it confirms compliance with Japanese electrical and safety standards.
Domestic Market Dial TextJapanese text printed on watch dials indicating features or specifications in the domestic language. Common examples include characters for water resistance, automatic winding, or material type on JDM-exclusive models.
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Frequently asked questions
What is the module number on my Casio watch?
The module number is a four-digit number typically found on the case back of your Casio watch. It identifies the electronic module (movement) inside the watch and can be used to find the user manual on Casio's website. The module number is often more useful for identification than the serial number.
How can I find the user manual for my Casio watch?
Casio maintains an online database of user manuals accessible through their website. By entering the four-digit module number found on your case back, you can typically download or view the complete manual for your watch. This is one of the most comprehensive resources for understanding your specific model's features and functions.
How do I know if my G-Shock is real?
Authenticating a G-Shock often involves checking the quality of construction, the clarity of case back markings, the module number's consistency with the model reference, and the overall weight and feel of the watch. Genuine G-Shock watches are known for precise assembly and robust build quality. Purchasing from authorized dealers is the most reliable method of ensuring authenticity.
What do the letters in a G-Shock model number mean?
G-Shock model numbers typically begin with letter codes that indicate the series or product line. For example, 'DW' often indicates a digital model, 'GA' typically indicates an analog-digital model, and 'GW' commonly denotes models with Multi-Band 6 radio wave reception. The numbers following the letters identify the specific model, and the suffix usually indicates the color variant.
Where are Casio watches made?
Casio watches are manufactured in several locations, with Japan, China, and Thailand being the most common assembly locations. Premium models and some special editions are often assembled in Japan, while more affordable models may be assembled in other facilities. The country of assembly is typically indicated on the case back.
How can I tell how old my Casio watch is?
Dating a Casio watch typically involves identifying the model reference number and looking up its known production period in collector databases or Casio's product history. Some watches include a date code on the case back or inside the battery compartment. G-Shock collector communities maintain particularly detailed production date information.
What does 'WR20BAR' mean on my Casio watch?
The 'WR20BAR' marking indicates water resistance to 20 bars (approximately 200 meters). This rating is commonly found on G-Shock and other sport-oriented Casio models. As with all water resistance ratings, the actual protection can degrade over time as seals age, and the rating applies to static pressure rather than dynamic forces like those from a running faucet.
Can I replace the battery in my Casio watch myself?
While battery replacement is technically possible for many Casio quartz models, it is commonly recommended to have it done by a qualified professional, particularly for water-resistant models. Opening the case back improperly can damage the water resistance seals. The module number on the case back can help identify the correct replacement battery, and Casio's manual database often lists the specific battery type.
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