COA Units & Conversions: % ↔ mg/mL ↔ mg/g (THC‑Free Context)

Q: Why don’t my label mg match the COA exactly?

Testing has normal variability and rounding. Check measurement uncertainty, method, and batch identity.

Q: How do I estimate per‑serving amounts quickly?

Convert to mg/mL or mg/g, multiply by serving size (mL or g), then compare to the label.

Q: What if THCA is listed but Δ9‑THC is ND?

Confirm both are ND (or below LOQ) and review “Total THC” calculations. If THCA is measurable, re‑evaluate risk and ask the brand for clarification.

Q: Can I rely on % alone?

Yes, with context. Convert % to mg/mL or mg/g and then to mg per serving. For gummies or caps, you need the per‑unit mass.

This practical cheat sheet consolidates COA unit conversions with a clear, conservative workflow to estimate cannabinoid amounts per serving—plus an integrated section on “Max THC per serving.” It is written for THC‑free shoppers and QA teams who use lab reports to verify non‑detectable THC (ND) at the lab’s Limit of Quantitation (LOQ). Educational only; not legal, medical, or employment advice.

Common COA units (what they mean)

% w/w: percent by weight (mg per g of product). 1% = 10 mg per g.
% w/v: percent by volume (mg per mL). 1% = 10 mg per mL.
mg/mL: milligrams per milliliter (common for oils).
mg/g: milligrams per gram (common for gummies, topicals, powders).
ppm: parts per million. For solids, 1 ppm ≈ 1 mg per kg (0.001 mg per g).

Quick conversion rules

% → mg/mL (liquids): mg/mL ≈ % × 10 (assuming density ≈ 1 g/mL).
% → mg/g (solids): mg/g = % × 10.
mg/mL → mg per serving: mg/mL × mL per serving.
mg/g → mg per serving: mg/g × g per serving.

Estimating mg per serving (step by step)

Find the unit on the COA (mg/mL, mg/g, %, ppm).
Convert to mg per container if needed: multiply by total mL or g.
Divide by servings on the label to estimate mg per serving.
Cross‑check label vs COA; expect minor variance within typical lab uncertainty.

Need a refresher on reading COAs? See How to Read COAs and Top Lab Testing Standards.

THCA → Total THC math (why 0.877 appears)

“Total THC” often equals Δ9‑THC + (THCA × 0.877). The factor 0.877 accounts for CO₂ loss when THCA decarboxylates to THC. For THC‑free verification, check both Δ9‑THC and THCA lines; both should be ND (or below LOQ) where applicable.

Max THC per serving (conservative, LOQ‑based)

When a COA reports Δ9‑THC as ND, the true value is below the method’s LOQ. A conservative estimate of maximum THC per serving is:

Max THC/serving ≈ LOQ (in mg per unit) × serving size.

Example: If LOQ is 0.001% w/w and a gummy weighs 4 g, per gummy max ≈ 0.001% × 10 mg/g × 4 g = 0.04 mg THC (conservative ceiling). For liquids reported in mg/mL with LOQ 0.05 mg/mL and a 1 mL serving, max ≈ 0.05 mg per serving.

Learn ND/LOQ nuances: LOQ vs. LOD and Non‑Detectable THC Claims: How to Verify.

Worked examples

Example A — Oil (mg/mL; ND at LOQ)

COA shows CBD 33 mg/mL, THC ND (<0.05 mg/mL). Label serving = 1 mL. Estimated CBD/serving ≈ 33 mg. Conservative max THC/serving ≈ 0.05 mg.

Example B — Gummy (% w/w)

COA shows CBD 0.8% w/w (i.e., 8 mg/g). Gummy mass = 4 g. Estimated CBD/serving ≈ 8 mg/g × 4 g = 32 mg. If THC ND with LOQ 0.001% w/w, max THC/serving ≈ 0.04 mg (as above).

Example C — Capsule (mg/g) with THCA listed

COA shows CBD 200 mg/g, THCA ND (<0.1 mg/g), Δ9‑THC ND (<0.1 mg/g). Capsule fill mass = 0.25 g. CBD/serving ≈ 200 × 0.25 = 50 mg. Max THC/serving ≈ 0.1 × 0.25 = 0.025 mg.

Example D — ppm in a topical

COA shows Δ9‑THC ND with LOQ 1 ppm. For a 60 g jar, conservative max THC/jar ≈ 60 g × 1 mg/kg ≈ 0.06 mg total.

Handling LOQ/ND conservatively

If multiple labs or methods vary, use the highest relevant LOQ for conservative ceilings.
Prefer COAs with clear units, method IDs, accreditation notes, and measurement uncertainty where provided.
When in doubt, contact the lab or brand for clarification.

Caveats, rounding, and density notes

Minor rounding differences are normal between label and COA.
Liquid density can deviate from 1 g/mL; when provided, use the product’s stated density for precision.
Batch variation exists; compare the exact lot code on your product to the COA.

FAQ

Why don’t my label mg match the COA exactly?