I count on my hands by twelve for basically everything, including breaths while meditating.
Here's how I do it!
Each of your fingers has three finger bones:
(1-2-3] : pointer (4-5-6] : middle (7-8-9] : ring (X-E-D] : pinky
Joining the finger bones of each finger are two knuckle bones.
And also each finger has a fingertip.
So when I'm counting on one hand, I drag my thumb from the fingertip toward the hand, counting 1 for each finger bone.
For counting breaths, what that looks like pausing on a fingertip or on a knuckle bone on an inhale, and then pausing on a finger bone on an exhale. (If you've ever counted prayer beads or a mala, it's basically the same thing.)
And then I count "one, two, three, four, five, six, seven, eight, nine, dek, el, do."
"Do" is like ten.
Once I have counted up to do, then I start counting on my second hand, one finger bone for every dozen I count on my first hand.
In this way, I time my sessions by breath. A "long" session is a dozen dozen breaths, or a gross. This takes me around 20 - 30 minutes.
And a short session is a half gross breaths. Or 6 do.
Now you know how to count to 12 (and 144) on your fingers!