Watch caseback markings: what the back of your watch means
Turn most watches over and you’ll find a small block of text: numbers, abbreviations, maybe a tiny stamp. Together they tell you what the watch is, what it’s made of and how much water it can take.
Short answer
A caseback typically carries the brand, a reference or model code, a serial number, the case material (“stainless steel”, a gold fineness like 750 for 18k), the water resistance (e.g. “WR 100M”, “10 ATM” or “10 bar”, all the same rating), and origin marks like “Swiss made”. Water resistance ratings are pressure tests, not dive depths: 30 m means splash-resistant only.
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Identification numbers
- Reference or model number: which model it is. See how to find a reference number for where each brand puts it.
- Serial number: which individual watch it is. It’s often used for dating and warranty.
- Movement or calibre code: some brands, notably Seiko and Casio, engrave the movement or module number on the back. It tells a watchmaker exactly what’s inside.
- Case number: older and vintage watches sometimes carry a case maker’s number that isn’t a model reference at all.
Water resistance
You’ll see it written several ways, and they mean the same thing: 10 ATM = 10 bar = 100 m = WR 100. The rating comes from a pressure test in a lab, not from an actual dive to that depth, and moving your arm through water creates extra pressure. As a practical guide:
| Marking | In practice |
|---|---|
| “Water resistant” / 30 m / 3 ATM | Rain, splashes and hand washing. Not swimming. |
| 50 m / 5 ATM | Brief swimming in a pool, at a push. No diving or snorkelling. |
| 100 m / 10 ATM | Swimming and snorkelling. |
| 200 m / 20 ATM and above | Recreational diving, usually on watches with a screw-down crown. |
| “Diver’s 200m” or ISO 6425 | A true dive watch built to the diver’s watch standard. |
Gaskets age, so a rating is only as good as the watch’s last pressure test. An older watch, or one whose case has been opened, shouldn’t be trusted in water until it’s been tested again. In detail: what each water resistance rating actually proves.
Case material
- “Stainless steel”, “Inox” (French/Italian) or “Acier” (French): a steel case. “Stainless steel back” alone can mean only the back is steel, with a plated base-metal case at the front.
- “Base metal” or no material marking: usually brass or alloy, often plated.
- “Gold plated”, “GP”, “RGP” (rolled gold plate), “GF” (gold filled), “10 microns”: a gold layer over another metal, not solid gold.
- Titanium: often marked “Titanium” or “Ti”.
Gold and silver hallmarks
Solid precious-metal cases are stamped with their fineness, in parts per thousand:
| Stamp | Means |
|---|---|
| 750 (or 18K, 18CT) | 18-karat gold, 75% gold |
| 585 (or 14K) | 14-karat gold, 58.5% gold |
| 375 (or 9K, 9CT) | 9-karat gold, 37.5% gold, common on older British watches |
| 950 | Platinum (Pt950) or silver (950), depending on the accompanying marks |
| 925 / 935 / 800 | Silver: sterling, and older continental grades |
Swiss solid-gold and silver watches often carry small official hallmarks too, such as the St. Bernard dog’s head for gold. British cases may have a full hallmark set with a date letter. A karat number alone, without a fineness stamp, deserves a second look from a jeweller.
Origin marks
- “Swiss made”: the watch meets Switzerland’s legal criteria for the label, which cover where the movement is made and assembled and a minimum share of Swiss manufacturing cost.
- “Swiss movement” or “Swiss parts”: only the movement or some parts are Swiss. The watch as a whole is not “Swiss made”.
- “Japan movt”: a Japanese movement, often in a watch assembled elsewhere.
Other things you might see
- “Screw back” or a toothed edge: a screw-down caseback, typically for better water resistance.
- “Automatic”, “Quartz”, “Solar”, “Kinetic”: how it’s powered. See automatic or quartz.
- Symbols: a helmet or wave icon for divers, and “Antimagnetic” for magnetic resistance.
- Engraved dedications on presentation watches. They lower resale to collectors but can add a lot of history.
Numbers worn away? Start from the dial
Loupe identifies a watch from a photo of the dial, giving the brand, model and reference where it can see them, with a confidence rating on every result. When it isn’t sure, it says so and suggests photographing the caseback too. Free trial, cancel in Google Play.
