The objective of this study was to assess the influence of the weight of the CORESTA monitor test piece on tar, nicotine, and carbon monoxide (TNCO) yields when it is smoked under the smoking regimes defined in ISO 3308 and Health Canada T-115. It was found that changing the weight standard deviation from 16 mg to 25 mg had no substantive effect on smoke yield variation in case of both linear and rotary smoking machines, even when constituent yields were affected by changes of monitor test piece weight in the case of rotary smoking machines. A standard deviation of individual monitor test piece weight of up to 25 mg has been estimated to give acceptable stability for the determination of TNCO.