Barrel Connector Measurement Tricks

At DigiKey, we receive many inquiries from people that need help finding barrel connectors, but when asked the inner diameter, they aren’t sure and have no way to measure it. Well here are a couple of tricks to decipher the measurement with common household items.

The most common outer diameter is 5.5 mm with two very common inner diameter (ID) measurements of 2.1 mm and 2.5 mm. These are very close and near impossible to take an accurate measurement with a ruler. So, if there’s not a caliper in sight, a toothpick, pen, or test lead can be used.

Toothpicks are commonly manufactured at a diameter of 2.1 mm to 2.2 mm. If it fits snug when inserted into the connector, then the ID is probably 2.1 mm, whereas if it falls out, then it’s 2.5 mm.

The widest point of a ballpoint pen should be between 2.25 mm and 2.35 mm. If the pen fits all the way to the widest point, the ID is 2.5 mm. If it only fits part way, then it is likely 2.1 mm.

Test lead probe tips are a little tricky to use, because they typically have a diameter of 2 mm. Since they will fit in both, you’ll need to identify if there is a noticeable gap making it 2.5 mm, or hardly any gap at all making it 2.1 mm.

If all of these tricks have been exhausted and you are still unsure, it is recommended to wait until a caliper can be used. They are the best tool for an exact measurement to ensure the proper part is purchased. Please watch our video for a demonstration.