What mg/mL means
Nicotine strength is expressed as milligrams of nicotine per millilitre of liquid. A 50 mg/mL liquid contains five per cent nicotine by volume. The number tells you concentration, not how much you will absorb — that depends on how often and how deeply you draw.
Salt nicotine versus freebase
Salt nicotine is buffered so it feels smoother in the throat at higher concentrations, which is why most pod and disposable devices use it. Freebase nicotine feels harsher at the same number, so it is normally used at lower strengths in open systems.
This is why a salt-nic device at a high number can feel gentler than a freebase liquid at a lower one. Comparing the numbers alone is misleading.
Signs you have gone too strong
Lightheadedness, nausea, a racing heart, headache or a scratchy throat usually mean the strength is above what suits you. Put the device down, drink water, and step down at the next purchase rather than pushing through.
Signs you have gone too weak
Chain-vaping without feeling settled generally means the strength is too low for you and you are compensating with volume. That burns through devices faster and tends to produce the dry, burnt hits described in the safety guide.
Read the label, every time
Strength is printed on the box and on the device. Do not assume two products in the same range share a strength, and never guess from flavour name or colour.