Tooth Numbering Calculator

Two Different Ways to Say "That Tooth"

Dental charts in the United States typically number teeth 1 through 32 under the Universal Numbering System, starting at the upper right third molar and working around to the lower right third molar. Most of the rest of the world uses the FDI (ISO 3950) two-digit system instead, where the first digit identifies the quadrant and the second identifies the position within it. A chart note referencing "FDI 36" and one referencing "Universal 19" can both be describing the exact same tooth — this calculator translates between the two notations directly.

The Formula

FDI quadrants run 1 (upper right) through 4 (lower right), with position 1 being the central incisor closest to the midline and position 8 being the third molar farthest back.

Where This Matters

• Reading dental records — translating between charts, referrals, or records that use different numbering conventions.
• International practice — dental offices working with patients or records from countries using FDI notation alongside US Universal numbering.
• Dental education — students learning to convert fluently between the two systems used across textbooks and clinical software.

Reference Conversion Table

The same 8-position pattern repeats for each quadrant: Universal 9–16 maps to FDI 21–28 (upper left), 17–24 to FDI 31–38 (lower left), and 25–32 to FDI 41–48 (lower right).

How to Use This Calculator

1. Choose the conversion direction: Universal to FDI or FDI to Universal.
2. Enter the tooth number in the source system (1–32 for Universal, or a two-digit FDI code like 18, 24, 36, 48).
3. Select Calculate to get the equivalent number in the other system, along with the tooth's common name.

Related Calculations

For estimating age from tooth development rather than identifying individual teeth, see the Dental Age Estimation Calculator, or plan treatment costs for a specific tooth with the Root Canal Cost Calculator.