What are ESN, HSN, and TSN?

The abbreviations you need to know about your car

If you own a car, or are thinking of buying one, you may have heard of emission key numbers (ESN), manufacturer key numbers (HSN) and type key numbers (TSN).

But what do they mean, and why do you require them? Here we explain the key numbers you need to find and use.


The key numbers are individual registration numbers for each vehicle registered by the Kraftfahrt-Bundesamt (KBA) in Flensburg.

They consist of letters and numbers (only numbers for older vehicles up to approx. 2005) and allow each vehicle to be clearly identified. The key numbers consist of the following elements:

  • To identify the manufacturer of the vehicle, there is the four-digit manufacturer key number (HSN), e.g. VW (0603), Ford (0928) or BMW (0005). It is used to uniquely identify the vehicle and to retrieve information about the manufacturer, such as the company name and address.
  • The model and version of the vehicle is indicated by the type code number (TSN), which consists of three letters and five digits (numbers only for older vehicles), e.g. AJO 00018 for a Škoda Octavia 1.2 TSI Combo.
  • It is used to uniquely identify the vehicle and retrieve model information such as name, engine, and equipment variants.
  • The emission standard of the car is indicated by the two-digit emission key number (ESN), e.g. 04 for Euro 4 or 14 for Euro 6d. This is a 17-digit number that identifies the vehicle’s exhaust emissions. It is used to determine the environmental performance of the vehicle and to calculate the amount of vehicle tax.
  • The key number or KBA number is the combination of HSN and TSN. The ESN is not part of the key number, but is often given together with it.


The key numbers are used for several purposes, including

  • You can use the key number to quickly and easily calculate the premium for your car insurance. Insurers use the code number to determine the type class of your vehicle, which reflects the accident and damage record of your vehicle model. In general, the lower the type class, the cheaper the insurance.
  • The key number allows you to calculate your vehicle tax when registering your vehicle. Vehicle tax depends on the engine capacity, exhaust emission standard and CO2 emissions of your vehicle, which can be determined from the key number.
  • If you are looking for spare parts or accessories, you can use the key number to find the right product for your car. The key number will help you avoid mistakes and save time when ordering.
  • In the event of a recall or warranty claim, you can use the key number to check if your car is affected.
  • To find vehicle information such as make, model, engine capacity and fuel type


You can find the key numbers on the Registration Certificate Part 1, the former vehicle registration document. The HSN is in field 2.1, the TSN is in field 2.2 (the first three digits) and the ESN is in field 14.1 (the last two digits). If you do not have access to your registration certificate, you can try to look up the key numbers online.

There are several websites that can help you find the HSN and TSN by make, model, and year. You can also request them from the registration office or your car dealer. You can often find the ESN using the KBA CO₂ calculator.


The key numbers are important information for every driver or car buyer.

They help you to uniquely identify your vehicle and take care of various matters relating to your car.