Painting - Is there really such a thing as one coat coverage?

I am about to paint a basement suite in a rental unit. I have bought one-coat paint before but always seem to need two coats either because of shading issues or see-through in some areas. One thing I have learned from this forum is that the 10mm roller I used all these years was not the best idea. Was that my problem?
I plan to use a similiar colour as whats existing but it won't be exact. Its a light blue.

"Is there really one-coat coverage paint"?

I've never found it.

If it means covering itself with one coat, sure. But for any color/sheen/product change, one coat ain't going to cut it IMHO.

Is there really such a thing as one coat coverage?

Not like what you are thinking, no

One thing I have learned from this forum is that the 10mm roller I used all these years was not the best idea. Was that my problem?

Probably not your problem with the one coat, no

Really if there was a true "one-coat" we would be all over that
I just chuckle everytime I hear that
Technically the surface may be "covered" with paint
But for needing only one coat to change the color of a room and/or look good over older paint...
I've never seen it

Would that it were true though....man that'd be great

It is a marketing strategy to call paint or rollers "one coat only". Typically, 2 coats are a minimum, but certain colours like reds, require 3 or 4.

Technically you can get 1 coat coverage but it requires a completely even film of paint at the specified thickness. Almost impossible to do. Any good paint should cover in 1 coat if the color change is minimal. This does not always apply to yellows and pinks.

Another reason why "one coat" is impossible is that less paint is applied using a brush during cutting then with the roller. Cut lines are very visible after only one coat.

Thanks guys. My mind is at ease.