- National Ambient Air Quality Standards (NAAQS)
- National Institute of Standards and Technology (NIST)
- National Physical Laboratory (NPL)
- Netherlands Measurement Institute (NMI)
- NEVOC
- NIOSH
- NIST-Traceable Reference Material (NTRM)
- Nitrogen Phosphorous Detector (NPD)
- Nitrox
- NMR
- NMRI
- Non-flammable gas
- Non-liquefied gas
- Non-refillable container
- Normal Boiling Point (NBP)
- Normal Evaporation Rate (NER) - Cryogenic
- Normal Temperature and Pressure (NTP)
- NPT
- Nuclear counters