11/15/2025
The normal range of mouth opening (also called maximum interincisal opening) is typically measured either in millimeters or in finger widths.
Clinical summary
* Normal: ≥40 mm (≈3 fingers)
* Mild restriction: 30–39 mm (≈2 fingers)
* Moderate restriction: 20–29 mm (≈1.5 fingers)
* * Severe restriction (trismus): ≤20 mm (≈1 finger or less).