Electronic cigarettes (also known as e-cigarettes or Electronic Nicotine Delivery Systems – ENDS), are a new type of product rapidly gaining popularity with adult cigarette smokers. They typically produce a condensation aerosol by quickly evaporating a formulation containing nicotine and water with glycerol, propylene glycol (PG) or a mixture of each. This study sought to measure droplet size distributions by real-time analytical methods using commercially available equipment. Measurements were conducted by electrical mobility (EM: Model DMS-500 MkII, Cambustion, UK) and by laser diffraction (LD: Spraytec, Malvern, UK). The Smoking Cycle Simulator (SCS: Cambustion, UK) was used to generate appropriate puff profiles, and to minimise dilution and potential droplet evaporation. Core profiles included 50, 55, 70 and 80 mL puffs of 3 s duration every 30 seconds. Volume-weighted median droplet diameters (d₅₀) from a variety of e-cigarette devices were typically less than 500 nm by LD and less than 300 nm for EM, slightly larger than equivalent tobacco smoke measurements of approximately 210 nm. The electrical mobility data were larger than previous published data suggesting evaporation was in part suppressed. Precision data were dependent on the e-cigarette tested but coefficients of variation of less than 4-5% were observed for the better performing products. This degree of precision meets the acceptance criteria for droplet size distribution (d₅₀ ± 20% for d₅₀ < 1 µm) for laser diffraction measurements for similar aerosol products. No equivalent standards are available for electrical mobility measurements. In conclusion, droplet size measurement for e-cigarettes can be readily achieved using commercially available sampling and measurement instrumentation, with suitable precision for product comparisons and to meet any potential regulatory requirements.