How this calculator works
Age-based formulas provide starting estimates, not a guaranteed fit or position. The uncuffed diameter is age/4 + 4 mm; the cuffed estimate used here is age/4 + 3.5 mm. Oral depth is age/2 + 12 cm measured at the lips. The unrounded estimates are shown because available tube sizes and device designs vary. Neonates and infants require separate equipment guidance, and this page does not extrapolate these formulas to them. The result is an estimate for information only and is not medical advice.
Formula
Uncuffed internal diameter (mm) = age/4 + 4. Cuffed internal diameter (mm) = age/4 + 3.5. Initial oral insertion depth at lips (cm) = age/2 + 12. Age is in years.
Worked example
At 8 years, the estimates are 6 mm uncuffed, 5.5 mm cuffed and 16 cm at the lips. At 4 years they are 5 mm, 4.5 mm and 14 cm.
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Frequently asked questions
Is this suitable for a newborn?
No. The age formulas here are restricted to children older than 2. Neonatal size and depth depend on separate gestational-age and weight guidance.
Does the depth confirm correct placement?
No. Confirm tracheal placement and appropriate tip position using the required clinical and monitoring methods. Age estimates cannot replace confirmation.
Should I round the diameter?
The calculator displays the formula result. A trained clinician must choose the available device size and prepare alternatives according to local guidance.