Barrel connectors are described by two numbers: the outer diameter and the inner diameter, both in millimetres. Getting either wrong means an adapter that will not fit, or one that fits loosely and cuts out. This chart lists what we actually stock and how to identify yours.

Connector sizes in stock, with real counts

How to measure your barrel connector

  1. Measure the outer diameter of the metal barrel, across the widest point.
  2. Measure the inner diameter of the hole – this is the pin inside the laptop socket.
  3. Write it as outer x inner in millimetres, for example 5.5 x 2.5. A caliper gives the reliable result; a ruler tends to round up.
  4. Check for a centre pin inside the plug. Some Dell and HP units use it for adapter identification.

Frequently asked questions

Are 5.5x2.5 and 5.5x2.1 interchangeable?
Often they are, because many sockets accept both, but a 2.1mm pin in a 2.5mm hole can spin loose. Check first.

Can I use an adapter with a centre pin in a plain socket?
Sometimes yes, but the identification signal may not be read, which can reduce charging speed.

My connector is not round. What is it?
It is likely USB-C, a Lenovo slim tip, a magnetic Surface connector or a proprietary plug; none of these are interchangeable.

Need the full background? Read our voltage and current guide and the complete laptop charger compatibility guide.