Pure nicotine is 1,000 mg/mL. 1% of 1,000mg/mL is 10mg/mL... regardless of what other ingredients are present. Sometimes one will see it stated as "
X% to volume." The "1%" is in reference to its pure state, and not a reference to the actual concentrate used (such a 100mg/mL concentrate, commonly used in DIYing
e-liquid).