Percentages vs Milligrams: Reading Concentration and Amounts

Why labels use different units

Cannabinoid products state strength in different ways. Dried plant material is often described as a percentage. Oils and liquids are often described as milligrams (mg) per container or per milliliter (mL). Edibles are often described as mg per piece. The units are not interchangeable without a little arithmetic, and each answers a different question. This page explains the arithmetic so labels can be read accurately. It never suggests how much to use, and a number on a label is not a recommendation.

The basic conversions

• Percent to mg per gram. One percent of a gram is 0.01 g, which is 10 mg. So a product that is 1% by weight holds 10 mg of that compound per gram. This is arithmetic, and it assumes the percentage is by weight.
• Per unit to per container. Multiply the per-unit amount by the number of units. Health Canada's label guide gives an example: a package of 4 edible pieces labeled "Total THC per unit 2.5 mg" contains 10 mg of THC. [1]
• Per gram to per package. Health Canada's example: a 30 g package labeled "Total THC 180 mg/g" contains 5,400 mg of THC (180 mg multiplied by 30 g). [1]
• Per container to per milliliter. Divide the total milligrams by the volume in mL. A bottle of oil that says 300 mg total in 30 mL is 10 mg per mL. Invented example, for arithmetic only.

Per-serving versus per-container

A single label can show several figures. A per-serving figure describes one stated serving. A per-container figure describes everything in the package. The two can differ by a large factor, and a container-level number can look reassuring or alarming depending on which one you read first. Health Canada's guide shows exactly this calculation for packages of several pieces: the whole-package amount is the per-unit amount times the number of pieces. [1] Always check how many servings or pieces the package contains before comparing products. The related guide on oil concentration and label interpretation works through liquids, and THC edibles covers why amounts and effects differ.

What cannot be converted

• A flower percentage cannot tell you what an edible contains, and the reverse. Different forms, routes and cannabinoid forms apply.
• Total THC on flower is a calculated potential value. See total THC and total CBD. The actual amount delivered by any use is not given by the percentage.
• Volume and weight are not the same. A percentage by weight does not become mg per mL without knowing the density of the liquid. Labels that state mg per mL already did this step; do not redo it from a percentage.
• Labels can be wrong. In a Colorado study of 277 flower and concentrate products, observed THC was significantly lower than labeled in both types. [2] A separate study of seized UK edibles found a median THC amount per edible of 13.71 mg, shown only as what that study measured in that illicit sample set and not as any normal amount. [3]

Safety note

Amounts printed on a package are not guidance for safe use, and sensitivity varies. If a child or pet swallows a cannabis product, treat it as urgent. In the United States, call Poison Help at 1-800-222-1222 or 911 for an emergency; see poisoning: what to do first and Poison Help by country. Questions about use with your medicines belong with your prescriber or pharmacist.