Before a nasogastric tube is inserted, it is marked at an estimated insertion depth so the practitioner can advance it to approximately the right length in one controlled pass. That mark is a starting point only — correct gastric placement must always be confirmed before any feed or medication is given through the tube. This tool calculates the starting estimate using two validated adult methods.
The two methods
NEX (Nose-Earlobe-Xiphisternum)
The practitioner holds the tube tip at the patient’s earlobe, measures to the tip of the nose, then continues to the xiphisternum (the lower tip of the sternum). The summed distance is the insertion length to mark on the tube. This is purely a measurement you take at the bedside — the tool records the value you enter.
Height-based formula
Studies have found that in some adult patients the NEX measurement underestimates the true gastric path, leaving the tube tip in the oesophagus. A height-based formula addresses this:
insertion length (cm) = height (cm) × 0.25 + 6.5For a patient 170 cm tall: 170 × 0.25 + 6.5 = 42.5 + 6.5 = 49 cm. A NEX on the same patient might read 53–56 cm. The two methods occasionally diverge meaningfully; local policy should specify which to use and how to handle disagreement.
Confirming placement — critical steps
The estimated length is never a confirmation. NICE guidance and most ward policies require:
- Aspirate pH test: withdraw a small volume of gastric content and test with pH indicator paper. A pH of 5.5 or below indicates gastric placement and is the recommended first-line confirmation method.
- Chest X-ray: used when pH is 6 or above (inconclusive), when there is no aspirate, or when the patient is at high risk (e.g. altered consciousness, swallowing difficulty, recent gastric surgery). The X-ray must be interpreted by a trained clinician before the tube is used.
Do not confirm placement by the auscultation method (listening with a stethoscope while air is injected) — this method has been associated with misplacement incidents and is no longer recommended as a confirmation test.
Why the estimate matters clinically
Getting the initial insertion length roughly right matters for two reasons. First, an under-marked tube may be advanced too far and coil in the oesophagus before the mark is reached, making misplacement harder to detect. Second, an over-marked tube may be pushed past the pylorus into the duodenum, which changes the aspiration characteristics and can yield pH readings that are falsely reassuring.
Marking the tube at a calculated estimate, advancing smoothly to that mark, and then following the confirmation protocol keeps risk low without requiring multiple blind adjustments at the bedside.
Comparing the two methods in practice
The table below illustrates how NEX and the height formula may compare for adults of different heights. These are illustrative figures only; actual NEX measurements depend on the individual patient’s anatomy.
| Patient height | Height-based estimate | Typical NEX range |
|---|---|---|
| 155 cm | 45.3 cm | 50–54 cm |
| 170 cm | 49.0 cm | 53–57 cm |
| 185 cm | 52.8 cm | 56–60 cm |
When the two methods produce meaningfully different values, local policy should be consulted. Some units use the shorter of the two estimates; others specify that the height-based formula applies in adults where NEX is suspected to underestimate.
Common pitfalls in adult NG tube placement
Using auscultation alone. Listening to air entering the stomach through a stethoscope is not an accepted confirmation method. Air can produce similar sounds even when the tube tip is in the bronchus. This method has been associated with fatal misplacement incidents and must not be used as the sole or primary confirmation test.
Skipping pH testing when aspirate is obtained. If a volume of aspirate can be obtained, pH testing with appropriate indicator strips takes only seconds and is the recommended first confirmation step. A pH above 5.5 should trigger further investigation.
Assuming position is stable after initial confirmation. Tube position can change with patient movement, vomiting, or coughing. Any time there is clinical concern, re-confirm position before use.
Scope of this tool
This estimator is intended for adult patients and ward or intensive-care nursing use. It does not apply to paediatric patients, for whom age- and length-specific paediatric charts are required. It does not confirm placement and should not be used as a substitute for clinical assessment and local NG tube insertion policies.