Fingerprint impressions can be usefully clustered into several pattern types: arches, loops, and whorls, with subclasses inside each. Pattern classifications are used for fingerprint images only, and do not apply to palms, lower joints, extreme tips, or plantar impressions.

Pattern classification of fingerprints follows the NCIC Classification, an extension of the Henry system. The table below summarizes the possible classes and subclasses of fingerprint patterns, and when to mark special cases. In broad terms, patterns are divided into three types: arches, loops, and whorls. Detailed instructions on pattern classification can be found in the Science of Fingerprints handbook and the Fingerprint Training Manual, and are further discussed in The Fingerprint Sourcebook.

A loop is a friction ridge flow pattern in which one or more ridges enter upon one side, recurve, touch or pass an imaginary line between delta and core, and pass out upon the same side the ridges entered. In the Extended Feature Set, loops are divided into two subclasses: left slant loops and right slant loops. Left loops have recurving ridges that point downward and to the left of the core, while right loops have recurving ridges that point downward and to the right of the core. Loops always have at least one intervening ridge between the core and the delta. The innermost recurve defines the presence of a core.

Arches have two subclasses: plain and tented. Plain arches have ridges which enter on one side of the impression and flow out the other with a rise or wave in the center. Tented arches possess either an angle, an upthrust, or two of the three basic characteristics of a loop. Cores may be marked on tented arches if an innermost recurving ridge is present above the delta, so that the sides of the recurving ridge extend to either side of the delta. Tented arches should have deltas marked, if such a structure is present. Note that tented arches may be similar to a loop, except that they lack one of the three requirements (recurve, delta, or ridge count).

The whorl is that type of pattern in which at least two deltas are normally present, with a recurve in front in each. (Some Accidental Whorls are exceptions and may not have two fully-defined deltas.) Subclasses of whorls are defined by the ridge flow within their cores:

• Whorl – Plain – A type of fingerprint pattern which consists of one or more ridges which make a complete circuit, with two deltas, between which, when an imaginary line is drawn, at least one recurving ridge within the inner pattern area is cut or touched. A plain whorl will have one core without any direction if the pattern is circular and two cores with direction if the pattern is elliptical.
• Whorl – Central Pocket Loop – A type of fingerprint pattern which at least one recurving ridge or an obstruction at a right angle to the line of flow. The pattern has two deltas between which, when an imaginary line is drawn, no recurving ridge within the inner pattern area is touched or cut. A central pocket loop whorl may have one or two cores depending on whether the pocket is circular or elliptical.
• Whorl – Double Loop – A type of fingerprint pattern that consists of two separate loop formations with two separate and distinct sets of shoulders, two cores, and two deltas.
• Whorl – Accidental – A fingerprint pattern consisting of two different types of patterns, with the exception of the plain arch, with two or more deltas; or a pattern which possesses some of the requirements for two or more different types; or a pattern which conforms to none of the definitions.

Classification must be conservative: if the pattern is known precisely, indicate only a single pattern; however, if there is any doubt as to the precise classification, include all possible patterns. If the pattern cannot be classified, but a pattern type can be definitively excluded, then indicate that by selecting all possible patterns. For example, if the image contains a delta, but the image cannot otherwise be classified, include all pattern classifications except the plain arch.

The information summarized in the accompanying Table is further described as follows:

1. General Class indicates the basic pattern classifications (arches, whorls, loops).

2. Subclass indicates the subcategories of the general class, which applies only to arches and whorls. Indicate this information item only if the subclass can be determined precisely or if specific subclasses can be excluded.

3. Whorl Delta Relationship may optionally be used by a human examiner or automated system to provide the relationship between the deltas in a whorl. Include this information item only for whorls whose subclass is known and only if the whorl delta relationship can be determined precisely. Set this information item to I (Inner), O (Outer), or M (Meeting), following the Henry guidelines (detailed in The Science of Fingerprints, p. 67). The information item is Inner if the ridge emanating from the left delta passes three or more ridges above (inside) the right delta and is Outer if the ridge emanating from the left delta passes three or more ridges below (outside) the right delta; otherwise, it is Meeting.

Up to seven pattern classifications may be indicated (including subclasses).

If scars or dysplasia are present but do not prevent the classification of the print, use the regular pattern class. Only use the Complete Scar (SR) or Dissociated Ridges/Dysplasia (DR) codes if the fingerprint cannot be classified.

In the dropdown above the image at right, click the checkbox next to each pattern type that might describe the impression shown. The image may be clear enough that you can narrow it down to one pattern type, or you might only have enough information to eliminate some options. You may select between one and seven pattern types for each print. To check your answers, use the button at the bottom left.

EFS pattern classifications are defined as they are in the NCIC method (as documented in Science of Fingerprints and the Fingerprint Training manual). However, when the pattern classification is borderline, especially if the class would change due to the presence or absence of a "spoiled" innermost recurving ridge (a recurving ridge with an appendage or crossing ridge), both of the potential pattern classifications must be indicated.

Note that exercises are not provided for designating whorl-delta relationships.