It’s difficult to have a single, simple answer to this question, as there are multiple variables for thousands of coins. However, there are some general principles that will help you find the information you’re looking for.
Condition of the coin
One of the biggest variables with any coin is the condition. If the coin is mint or near mint condition, it will bring a much higher value than a damaged coin. To a coin grader or collector, damage can be very minor to the eye and still drastically affect the value of the coin. This is why most collectors do not clean coins that they find; even the most gentle wash is capable of scratching thin lines onto the surface of the coin. Coins are usually damaged from the rigors of circulation, where no special care is taken to protect them.
Rarity and Date
Another major factor is the rarity of a coin. A coin that was only minted in the thousands will often have a higher value than coins with mintages in the millions.
The date of a given coin can also be an indicator of rarity, and therefore of value. More coins may have been minted in one year than another, or the coins in a particular year are made of a different metal (for instance, the 1943 steel pennies).
The final major factor is the mint mark. This is a small mark on the coin, usually a single letter, that indicates which mint the coin originated at. United States mint marks are: Charlotte, North Carolina (C, gold coins only, 1838-1861); Carson City, Nevada (CC, 1870-1893); Dahlonega, Georgia (D, Gold coins only, 1838-1861); Denver, Colorado (D, 1906 to date); New Orleans, Louisiana (O, 1838-1909); Philadelphia, Pennsylvania (P, 1793 to date); San Francisco, California (S, 1854 to date); and West Point (W, 1984 to date.)
One thing to note is that denominations of coins have changed over the course of history; be sure you know the face value of the coin, when possible, to get more accurate information about the value of the coin.
Valuation, Grading, and Identification
Your best bet for getting a good valuation on your coin is to have it professionally graded: PCGS is an excellent resource, as is NGC. Once the coin is graded, it will be much easier to find a value for it. If you don’t wish to take your coin to a professional, there are a few forums and Facebook groups that may be able to help you. Here’s what you need to do:
- If you have a digital camera, use that to take the picture. If you don’t, a decent smartphone will work, if you are careful.
- Light the coin well, making sure to light from several angles to eliminate shadows and glare.
- Position the coin on a blank background, preferably either black or white.
- Use a tripod, if you have one. The more fine detail you can capture, the better. If you don’t have a tripod, try to brace the camera or phone against something solid while taking the photo.
- Get as much information about the coin as you can. If you know the country, denomination, etc, include that information with the photo. If the coin doesn’t come with that information, a Google Image search may be helpful.
Once you have the photo and information, share it with the group. You are likely to get some conflicting answers, and will still need to do your own research, but this can give you a good place to start. Once you know what kind of coin you have, you can look it up in the Red Book or other guide to get a more precise valuation.
The information from a group or forum should never be considered as a professional evaluation, but if you just want more information about a coin you happened across, it can be a great resource.