Potency Units Explained: Percent, mg/g, mg/mL, and Milligrams per Container
A cannabinoid number is incomplete without its unit and its basis.
“25 mg,” “25 mg/mL,” “25 mg/g,” and “25%” do not describe the same quantity. One can be an amount in a serving or container, another a concentration in liquid, another a mass fraction in a solid, and another a percentage of mass.
The arithmetic is straightforward once the label or laboratory report answers three questions:
- What is being measured? CBD, THCA, delta-9 THC, total THC, or something else?
- What is the denominator? A gram, milliliter, serving, package, or submitted sample?
- What is the basis? By mass, by volume, dry weight, or as received?
This guide explains the units. It does not recommend a serving or dose.
The four common views
| Expression | What it usually describes | Read it as |
|---|---|---|
| % | Mass fraction in plant material or another solid, when reported by mass | Parts per hundred by mass |
| mg/g | Mass of a named compound per gram of material | Milligrams in each gram represented by the result |
| mg/mL | Mass concentration in a liquid | Milligrams in each milliliter |
| mg per container | Total labeled amount in the complete package | Package amount, not concentration |
The words around the number control the interpretation. A “30 mL bottle” states volume. “1,500 mg CBD” may state a total amount for the bottle. “50 mg/mL CBD” states concentration. None of those statements alone establishes what a laboratory measured.
Start with milligrams and grams
The metric prefix milli- means one-thousandth:
1 gram = 1,000 milligrams
NIST's Guide to the SI uses g for gram and mg for milligram. Unit symbols are case-sensitive; there should be a space between the value and unit in formal technical writing, such as 25 mg.
When a laboratory reports 12 mg/g, it is expressing a mass of the named compound relative to a gram of the tested material. If the result represents the material in question, the arithmetic for 3.5 g is:
12 mg/g × 3.5 g = 42 mg
The grams cancel, leaving milligrams. This calculation does not prove that every part of a package is uniform or that the submitted sample represented every unit.
Converting percent by mass and mg/g
For mass fractions:
1% = 1 g per 100 g
Because 1 g equals 1,000 mg:
1% by mass = 10 mg/g
That gives two useful conversions:
percent by mass × 10 = mg/g
mg/g ÷ 10 = percent by mass
Examples:
| Percent by mass | Equivalent mg/g |
|---|---|
| 0.3% | 3 mg/g |
| 1.0% | 10 mg/g |
| 1.8% | 18 mg/g |
| 10.0% | 100 mg/g |
| 25.0% | 250 mg/g |
This conversion is valid only when the percentage and mg/g value use the same mass basis. A dry-weight percentage cannot automatically be compared with an as-received result that includes moisture.
Percent needs a stated basis
A percent sign means “per hundred,” but it does not identify what the numerator and denominator are.
Laboratory cannabinoid results for plant material are commonly mass fractions. A report may state %, % w/w, mass %, dry weight, or as received. Those qualifiers matter.
- Percent by mass compares compound mass with material mass.
- Percent by volume compares volumes and is a different quantity.
- Dry-weight basis excludes moisture according to the stated method or calculation.
- As-received basis describes material in the condition analyzed, moisture included.
Do not convert between dry-weight and as-received results without moisture data and the laboratory's stated basis. The same sample can have different numerical concentrations when expressed on different moisture bases without the amount of cannabinoid changing.
NIST's hemp reference-material work reports cannabinoid mass fractions and documents the material and measurement conditions. That specificity is what makes the number interpretable.
Milliliters describe volume
NIST explains that a milliliter is a special name for a cubic centimeter and that 1,000 mL equals 1 L. For an oil or other liquid, bottle size is commonly expressed in milliliters.
Volume is not cannabinoid amount. A 30 mL bottle and a 60 mL bottle can contain the same total milligrams at different concentrations, or different totals at the same concentration.
When a label gives both total cannabinoid amount and bottle volume:
mg/mL = total mg ÷ total mL
Hypothetical example:
1,500 mg CBD ÷ 30 mL = 50 mg/mL CBD
A 60 mL bottle containing the same 1,500 mg total would be:
1,500 mg CBD ÷ 60 mL = 25 mg/mL CBD
Both bottles have the same labeled total. The first has twice the labeled concentration.
From mg/mL to a measured volume
When liquid concentration and a measured volume are known:
amount in measured volume = mg/mL × mL
Hypothetical example:
25 mg/mL × 0.5 mL = 12.5 mg
This calculation requires an actual volume. “One dropper” is not a technical volume unless the package defines it and the measuring device supports it. Droppers can have markings, and fill level can vary.
Arithmetic from a label also does not establish that the product contains the labeled concentration. That requires appropriate product testing, sampling, and documentation.
Milligrams per container are not concentration
“1,000 mg per bottle” is a package total. It does not show concentration until bottle volume is known.
Compare three hypothetical labels:
| Total amount | Bottle volume | Calculated concentration |
|---|---|---|
| 1,000 mg | 20 mL | 50 mg/mL |
| 1,000 mg | 30 mL | 33.3 mg/mL |
| 1,000 mg | 60 mL | 16.7 mg/mL |
The total remains 1,000 mg, but the amount per milliliter changes. Rounded results should remain visibly rounded; 1,000 ÷ 30 does not justify printing an endless decimal.
For a package containing multiple units, “per piece,” “per serving,” and “per container” must also remain separate. Ten pieces labeled 10 mg each would imply 100 mg across those ten pieces, provided the unit amount and count refer to the same named compound. It does not follow that every piece was tested individually or is perfectly uniform.
Build the quantity map before calculating
A useful way to avoid mixing quantities is to write each label statement on its own line before using a calculator.
Consider a hypothetical liquid package that states:
- bottle volume: 30 mL;
- labeled CBD total: 900 mg per bottle;
- labeled serving volume: 1 mL; and
- 30 servings per bottle.
The concentration calculation is:
900 mg ÷ 30 mL = 30 mg/mL
The amount in the labeled 1 mL serving is then:
30 mg/mL × 1 mL = 30 mg
The serving count provides a cross-check:
30 servings × 30 mg per serving = 900 mg per bottle
Agreement shows that the printed quantities are arithmetically consistent. It does not verify the formulation or substitute for testing.
Now suppose the same package says “one serving” but does not state a serving volume. The total and bottle volume still allow calculation of 30 mg/mL, but the amount per serving cannot be calculated from the available information. A serving is a declared portion, not a universal metric unit.
For a solid package, the map might contain net weight in grams and a COA result in mg/g. Multiplying can estimate the corresponding amount only if the COA result represents that package material and uses the same basis. If batch identity, moisture basis, or net mass is missing, label the calculation incomplete rather than filling the gap with an assumption.
Why mg/g and mg/mL do not directly convert
Milligrams per gram uses mass in the denominator. Milligrams per milliliter uses volume.
A direct conversion requires density or a measured mass-volume relationship for the material:
density = mass ÷ volume
It is unsafe to assume that 1 mL of every oil weighs exactly 1 g. Water is often used as an intuitive reference, but oils and formulated products can have different densities. Temperature and composition can also affect volume and density.
If a label gives only mg/g, do not rewrite it as mg/mL. If it gives only mg/mL, do not rewrite it as mg/g. Preserve the reported unit unless the necessary additional measurement is available.
A COA and a package label answer different questions
A certificate of analysis reports laboratory results for a submitted sample. A package label describes the product offered for sale and may state formulated or declared values.
Before comparing them, check:
- product and batch identity;
- sample matrix;
- date received and date analyzed;
- whether the result is percent, mg/g, mg/mL, or a package claim;
- dry-weight or as-received basis;
- whether the laboratory calculated “total” values;
- reporting limits and qualifiers; and
- whether the label and report name the same cannabinoid.
A flower COA expressed in percent by mass should not be expected to look like an oil label expressed in total milligrams per bottle. Convert only comparable quantities.
Use How to Read a Hemp Certificate of Analysis for the full document-matching process.
“Total THC” adds a separate calculation
THCA and delta-9 THC are different reported analytes. A total-THC value may apply a molecular-weight conversion to THCA before adding delta-9 THC.
That calculation is separate from converting percent to mg/g. First identify whether the report presents THCA, delta-9 THC, calculated total THC, or all three. Then preserve the report's basis and units.
The formula and its legal contexts are explained in Total THC and THCA: The Calculation, the Context, and Its Limits.
Non-detect is not zero
Laboratory reports may use ND, <LOQ, <LOD, or a numerical less-than result. These refer to detection or quantitation limits under the laboratory's method.
They do not automatically mean absolute zero. Do not replace a qualified result with 0 mg, and do not use zero in a package-total calculation unless the report actually supports that treatment.
The number of decimal places also matters. A reported 0.10% does not become more certain because a calculator displays 1.000000 mg/g. Carrying reasonable precision prevents arithmetic from implying better measurement than the source.
A practical comparison checklist
Before comparing two potency statements, confirm:
- They name the same cannabinoid or calculated total.
- They use the same denominator—or you have enough information for a valid conversion.
- They use the same moisture or mass basis.
- The bottle volume, package count, or material mass is known.
- The values refer to the same product and batch when making a product-specific comparison.
- Less-than signs and laboratory qualifiers are preserved.
- Rounding does not invent precision.
If any item is missing, the honest result may be “not enough information to compare.”