How to Read Audemars Piguet Reference Numbers

When it comes to Audemars Piguet, few things separate casual fans from true collectors more than the ability to read and understand reference numbers. These strings of letters and numbers may look random at first, but they're actually a detailed system that reveals what model you're looking at, what material it's made from, and even the bezel, dial, or bracelet type.

Unlike brands such as Rolex, Audemars Piguet does not engrave its reference numbers on its watches. This means knowing how to decode an AP reference is particularly useful, especially if you're buying, selling, or authenticating one. Each AP reference follows a precise alphanumeric structure that identifies the model family (for example, Royal Oak, Royal Oak Offshore, or Code 11.59), the case material, and other defining characteristics.

Whether you're trying to confirm what's written on a warranty card or simply want to understand what makes a 15500ST different from a 15202OR, learning how to read Audemars Piguet reference numbers will give you a clearer view of the watch in front of you.

The Structure of Audemars Piguet Reference Numbers

Audemars Piguet reference numbers include 17 numbers and letters, and follow a consistent structure that breaks down into key segments:

Let's take the following reference as our working example: 15510OR.OO.1320OR.04

Here's how this seemingly complex alphanumeric string reveals everything you need to know about the watch:

Model Code (15510)

The first five digits indicate the specific model family. In this case: 15510 = Modern Royal Oak Selfwinding, 41mm.

This code changes depending on the size, complication, and design. For example, 16202 refers to the Jumbo Extra-Thin, while 26420 refers to a Royal Oak Offshore Chronograph, 43mm.

This is the most important part of an Audemars Piguet reference number — it's the shorthand you'll hear most often when models are referenced in writing or conversation.

Material Code (OR)

The next two letters are case material codes, which in our example is OR: 18k pink gold.

Common case material codes include:

• BA – Yellow Gold
• BC – White Gold
• CB – White Ceramic
• CD – Blue Ceramic
• CE – Black Ceramic
• CM – Brown Ceramic
• IO – Titanium and Ceramic
• OR – Rose Gold
• PT – Platinum
• RO – Rose Gold and Ceramic
• SA – Steel and Yellow Gold
• SG – Sand Gold
• SO – Steel and Ceramic
• SR – Steel and Rose Gold
• ST – Stainless Steel
• TI – Titanium

Bezel Code (OO)

The next set of letters is the bezel code, which in our example is OO or a standard, non-decorated bezel.

The most common bezel codes in Audemars Piguet reference numbers are:

• OO – Smooth Bezel
• ZZ – Diamond-Set Bezel
• YG/YY – Colored Gemstone-Set Bezel
• HH – Yellow Sapphire-Set Bezel
• GG – Frosted (Hammered) Gold Bezel

Bracelet/Strap Code + Material (1320OR)

The next six characters represent the bracelet or strap style and its material.

In our example, 1320 is the newest generation of the Royal Oak bracelet introduced in 2022, and again, OR refers to its pink gold construction.

Bracelet codes are four digits followed by two letters for metal bracelets. For non-metal straps, the codes usually begin with a letter, followed by numbers, and end in two letters.

While we already know what the metal codes are, some common non-metal material codes found in Audemars Piguet reference numbers include:

• CA – Rubber Strap, e.g., Royal Oak Offshore Ref. 26238ST.OO.A340CA.01
• CR – Leather Strap, e.g., Royal Oak Chronograph Ref. 26240OR.OO.D315CR.02
• KB – Rubber-Coated Strap, e.g., Code 11.59 Starwheel Ref. 15212NB.OO.A002KB.01
• VE – Calfskin Strap, e.g., Royal Oak Offshore Ref. 26420CE.OO.A005VE.01

Dial Code (04)

The last two digits in an Audemars Piguet reference number are the dial code, which in our example is 04.

These numbers don't refer to color or finish in a fixed way — instead, they're sequential. For example, .01 typically marks the initial dial version, while .04 means it's the fourth variation introduced for that particular model.

Where To Find Audemars Piguet Reference Numbers

Unlike serial numbers, which are engraved directly onto the caseback, Audemars Piguet reference numbers do not appear anywhere on the watch itself.

Instead, reference numbers are documented in accompanying materials such as the warranty card, Certificate of Authenticity, or product literature. You may also find them in official service papers, resale listings, or digital catalogs.

This can be confusing for those familiar with brands like Rolex, which engrave reference numbers somewhere on the case. With AP, knowing the reference number and how to decode it becomes especially important — not just for collectors and resellers, but also for buyers trying to verify what they're looking at.

Common Audemars Piguet Model Codes

As explained, the first five digits of an Audemars Piguet reference number are known as the model code, and they tell you the collection, complication, and case size of the watch.

This part of the reference is often what collectors and retailers use to refer to a watch — it's the primary identifier in most listings and discussions. For instance, you'll often hear people say "15500" or "26331" instead of the full reference.

Here are some examples of common Audemars Piguet model codes and what they represent:

• 15510 – Royal Oak Selfwinding, 41mm
• 15202 – Royal Oak "Jumbo" Extra-Thin, 39mm
• 15550 – Royal Oak Selfwinding, 37mm
• 77450 – Royal Oak Selfwinding, 34mm
• 26240 – Royal Oak Chronograph, 41mm
• 26674 – Royal Oak Perpetual Calendar, 41mm
• 26730 – Royal Oak Selfwinding Flying Tourbillon, 41mm
• 15407 – Royal Oak Double Balance Wheel Openworked, 41mm
• 26420 – Royal Oak Offshore Chronograph, 43mm
• 26238 – Royal Oak Offshore Chronograph, 42mm
• 15720 – Royal Oak Offshore Diver, 42mm
• 15210 – Code 11.59 Selfwinding, 41mm
• 26393 – Code 11.59 Selfwinding Chronograph, 41mm

Why Knowing Audemars Piguet Reference Numbers Matters

Whether you're buying your first AP or adding to a growing collection, being able to read and understand Audemars Piguet reference numbers is a valuable skill. It helps you decode key information about the watch's model, case material, bracelet style, and dial — details that aren't always obvious at a glance.

If you're shopping on the pre-owned or gray market, always ask to see documentation that confirms the reference number. It's one of the best ways to verify the exact configuration of the case, bracelet, and dial, especially when photos alone may not show enough detail to distinguish between variations.