INTRODUCTION: E-cigarette unit sales have been estimated using the number of items typically available in a package to standardize unit sales of each product type. However, recent market changes, such as increases in e-liquid volume and nicotine concentration, challenge the validity of assessing sales according to item count without accounting for product attributes. This study measured nicotine content (mg) in e-cigarettes sold as a function of e-liquid volume (mL) and nicotine concentration (mg/mL), compared with e-cigarette unit sales standardized by item count. METHODS: U.S. e-cigarette retail sales data from Circana (February 2019 to June 2024) were analyzed. Trends in mg nicotine sold were compared with standardized unit sales. Additionally, sales-weighted average e-liquid volume, nicotine concentration, and price per milligram of nicotine were measured by product type. Trends were assessed using Joinpoint regression. Analyses were conducted in 2024. RESULTS: From February 2020 to June 2024, monthly milligrams of nicotine content sold increased by 249.2% (p<
0.002)-an increase 7.2 times greater than the 34.7% increase in standardized unit sales. Disposable e-cigarettes experienced the greatest increase in mg nicotine sold, which was largely driven by the rise in e-liquid volume. By June 2024, a disposable device contained 9.0 times more e-liquid than a prefilled cartridge. However, the price per milligram of nicotine in prefilled cartridges was 3.7 times greater than that of disposable devices. CONCLUSIONS: Nicotine is an addictive drug added to most e-cigarettes. Measuring e-cigarette sales in milligrams of nicotine content sold could better account for rapid changes in product attributes and inform policy strategies.