Percent weight by weight

Percent weight by weight expresses how much of a product's total mass is made up of a particular substance, written as a percentage.

A figure of ten percent weight by weight means ten grams of the substance in every hundred grams of product. It is the standard way to report cannabinoid content in plant material and extracts, and it is the unit in which the federal hemp definition of 0.3 percent delta-9 THC is written. Unlike milligrams per container, it does not change with package size.

On a certificate of analysis for a finished product, the potency section often shows both a percentage and a milligrams-per-unit figure derived from it using the net weight or fill volume. Multiplying the percentage by the product mass gives the total cannabinoid content, which can then be compared with the label claim. Liquids are sometimes reported weight by volume instead, and the two are not identical because oils are lighter than water, so the unit label matters when comparing certificates.