How would you define the strength of a pinkie-promise?

Your word is your bond regardless of ritual or ceremony. Kids may be forgiven. It’s a luxury afforded their inexperience and consequent lack of judgment.

Useless as teats on a boar hog actually, but I always try to keep it to my grand daughters. They take it serious. Normally I can keep the promise, minus unusual unusual circumstances.

Generally, I’d say:

cross my heart and hope to die > pinky promise > I swear

But also depends on individual.

Kids are dead serious when they pinky swear. The pinky came along after my generation. We always used the Cross my heart, hope to die & to prove our sincerity, we added Stick a needle in my eye. I don’t remember any kid ever having to stick a needle in their eye as punishment. Fortunately kids’ attention span is very short & they really no longer cared by time you failed the Cross my heart pledge

It is deadly serious, but for one day only.

“I swear of my mother’s grave”, we said.
After which we broke the promise immediately.
My mom is still healthy.

As strong as the flimsy pinkies involved.