What is a normal outdoor water connection?

We have a "normal" water tap outside. Now I want to buy a hose that is offered at the local discount store. Is it probably 3/4 inch or 1/2 inch? What is the common size? Of course, I could also call the plumber, but he might be annoyed.

One could also simply measure?

One could now be quite daring and hold a ruler to the connector...

Ok. So 1.9 cm or 1.27 cm. Inner diameter?

Um, yes. Customs in centimeters... feasible task.

I know. But the construction site is 14 km away. The offer says "Außenwandventil Eurotec DN 15". That doesn't help me either.