Grading guides for United States coinage can be found on this website in articles titles; Grading Circulated U.S. Coins and Grading Uncirculated U.S. Coins
There are no uniform guides for world coins. What follows is an attempt to help bridge the gap until a detailed, illustrated guide becomes available.
In grading world coins, there are two elements to look for: 1) Overall wear, and 2) loss of design details, such as strands of hair, feathers on eagles, designs on coats of arms, etc.
The age or rarity of a coin should not be a consideration in grading
Grade each coin by the weaker of the two sides. This method appears to give results most nearly consistent with conservative American Numismatic Association standards for U.S. coins. Split grades, i.e., F/VF for obverse and reverse, respectively, are normally no more than one grade apart. If the two sides are more than one grade apart, the series of coins probably wears differently on each side and should then be graded by the weaker side alone.
When examining a coin, grade by the amount of overall wear and loss of design detail evident on each side of the coin. On coins with a moderately small design element, often prone to early wear, grade by that design alone. For example, the 5-ore (KM#554) of Sweden has a crown above the monogram on which the beads on the arches show wear most clearly. For this coin type you would grade by the crown alone.
Grading criteria for world coins
For MS-66 grade full mint luster will be present with no visible signs of any wear or handling, even under strong magnification. An above average strike and obvious, significant eye appeal are needed for assignment of this grade designation.
For MS-65 (Gem Brilliant Uncirculated, GemBU) grade there will be no visible signs of wear or handling, even under a 10-power loop. Full mint luster should be present, but is not a neccessity of the grade. No detracting bag or adjustment marks will be present. Sharp rims and bold detail are characteristic of this grade.
For MS-63 (Choice Brilliant Uncirculated, ChoiceBU) grade there will be no visible signs of wear or handling, even under a 10-power loop. Some mint luster should be present, but is not a neccessity of the grade. Ideally no bags marks will be evident, though light adjustment marks may be present.
For MS-60 (Uncirculated, Unc) grade there will be no visible signs of wear or handling, even under a 10-power loop. Adjustment marks and bag marks may be present.
For AU-50 (Almost Circulated, AU) all details will be visible. There will be the slightest of wear only on the highest point of the coin. There will often be half or more of the original mint luster present.
On the XF-40 (Extremely Fine, XF or EF) coin, there will be about 95% of the original detail visible. Or, on a coin with a design with no inner detail to wear down, there will be a light wear over nearly all of the coin. If a small design is used as the grading area, about 90% of the original detail will be visible. This latter rule stems from the logic that a smaller amount of detail needs to be present because a small area is being used to grade the whole coin.
The VF-20 (Very Fine, VF) coin will have about 75% of the original detail visible. Or, on a coin with no inner detail, there will be moderate wear over the entire coin. Corners of letters and numbers may be weak. A small grading area will have about 66% of the original detail.
For F-12 (Fine, F) there will be about 50% of the original detail visible. Or, on a coin with no inner detail, there will be fairly heavy wear over all of the coin. Sides of letters will be weak. A coin which has not been cleaned will often appear as dirty or dull. A small amount of the grading area will have just about 50% of the original detail.
On the VG-8 (Very Good, VG) coin, there will be about 25% of the original detail visible. There will be heavy wear over all of the coin surfaces.
The G-4 (Good, G) coin’s design will be clearly outlined but with substantial wear. Some of the larger detail may be visible. The rim may have a few weak spots of wear.
On the AG-3 (About Good, AG) coin, there will typically be only a silhouette of a large design. The rim will be worn down into the remnants of the letters of the legend.
Strong or weak strikes, partially weak strikes, damage, corrosion, fingerprints, attractive or unattractive toning, rim bumps, dipping or cleaning should be described along with the above grade. These factors affect the quality of the coin just as do wear and loss of detail but are easier to describe.
Countermarked and counterstamped coins are graded differently
When a punch is used to alter a coin after its original production it is considered countermarked. When the mark is applied by using a hinged pair of punches it is considered counterstamped. These two basic methods were used officially and unofficially for a number of purposes, but authentication or revaluation were the primary reasons.
A countermark or counterstamp creates a disturbance in the original design, making a "new" coin. Because of this idiosyncrasy, grading is completed on the countermark or counterstamps alone. The grading standards outlined above may not always apply adequately to marks and stamps, whether incuse or raised. Condition, clarity, and completeness have become the additional points by which we judge a countermark or counterstamp.
The grade of a countermarked or counterstamped coin is determined through an amalgamation of these various factors. But bare in mind that the "host" coins identification and preservation are definitely taken into consideration when assessing a value for the piece.
Proof coins are struck using specially prepared blanks and dies
The term proof indicates a method of manufacture and not a grade. Still, proof coins are graded but by quality of strike and not actual wear. PF-60, PF-63, PF-65, PF-67 or PF-69 are typical grades you will see for proof coins on our website.
In order to buy and sell proof coins at these designated grades, normally third-party grading and encapsulation is required. A high degree of magnification is used to determine strike quality and any imperfections are noted prior to the coin being assigned a grade and sealed in its capsule.
As the 21st century dawned, mints and distributors have employed special clean-room manufacturing processes which have virtually eliminated problems and imperfections in commemorative issue uncirculated and proof coins. The modern low mintage uncirculated or proof coin is often only available in sealed multi-coin sets, or encased within individual plastic holders within a fitted display case. This makes for nearly perfect coins.