% by weight

Percent by weight (w/w) is the standard potency unit for cannabis flower and solid concentrates, indicating the mass fraction of a cannabinoid (typically total THC, total CBD) in the sample. A flower COA listing "20% THC" means 20 g THC per 100 g of flower (200 mg THC per gram). ASTM D8375 specifies LC-MS/MS methodology for dried flower. Percent by volume (v/v) is occasionally used for cannabis-infused liquids but is far less common than mg/mL; ASTM best practice (D8449) recommends mg/mL for liquids to avoid ambiguity. Labeling inconsistency persists: some manufacturers report "% THC" on liquids without specifying w/w, w/v, or v/v, creating consumer confusion. Label accuracy is a documented problem: Vandrey et al. (2015 JAMA) found only 17% of edibles within ±10% of label; Schwabe et al. (2023 PLoS One) found Colorado flower labels over-reported THC by ~15%. Regulators are migrating toward mg-per-serving + mg/mL formats for all products. Citations: ASTM D8375-22; ASTM D8449; Vandrey R et al. JAMA. 2015;313:2491-2493; Schwabe AL et al. PLoS One. 2023;18:e0282396; Bonn-Miller MO et al. JAMA. 2017;318:1708-1709. ---