Coin grading is the most precise system in collecting and the one where a small difference in the number is a large difference in the money.
The scale
The standard numeric scale runs 1 to 70, with the circulated grades below 60 and the uncirculated grades from 60 upward. Descriptive names sit alongside the numbers — good, very good, fine, very fine, extremely fine, about uncirculated — and the gaps between the top grades are where most of the value lives.
What "uncirculated" has to mean
A coin that has never been in circulation. Not "looks new", not "barely worn" — never circulated. It is the single most misused word in the category, and misusing it is what turns a sale into an argument.
What is assessed
Wear on the highest points of the design, which is where circulation shows first. Strike quality, which is about how well the coin was made rather than how it was treated. Surface — marks, hairlines, and any evidence of cleaning. Eye appeal, which is real and is why two coins at the same number can differ in price.
Cleaning is not a grade
A cleaned coin is usually described as cleaned rather than given a straight grade, because cleaning removes original surface permanently. It is the one thing in this category that cannot be undone. Common mistakes.
Notes
Paper money is graded on its own ladder, with folds and crispness doing most of the work. An uncirculated note has no fold at all — including the central one.
If you do not grade
Give a band, say you are not a grader, and show the coin tilted under light so a buyer can judge. That is a respected listing.
Questions people ask
Is a graded holder worth the fee?
For scarce and high-grade coins, often. For common circulated coins, rarely.
Does toning lower a grade?
Natural toning is normal and can raise desirability. Corrosion is different.
Can I grade from a photograph?
You can form an opinion. Say that it is one.
More: describing coins, what they are worth.