Total THC calculator

Why total THC matters more than Δ9-THC

On a certificate of analysis, the Δ9-THC figure is often very low, for example 0.04 %. Yet hemp flowers mostly contain THCA, the acid form of THC. THCA has no effect as it is, but it turns into Δ9-THC when heated: smoking, vaporizing or cooking. This is called decarboxylation.

To know how much THC a product can actually release, labs calculate total THC with this formula: total THC = Δ9-THC + 0.877 × THCA. The 0.877 factor comes from molecular mass: when THCA loses its carboxyl group as CO₂, the molecule loses about 12.3 % of its weight. The same rule applies to CBD: total CBD = CBD + 0.877 × CBDA.

How to use the calculator

Pick the unit used on your certificate. Most labs report results in percent (%), some in mg/g. 1 % equals 10 mg/g. Then copy the Δ9-THC, THCA, CBD and CBDA lines. If a value reads "< LOQ" or "ND", leave the field empty: the compound is below the lab's limit of quantification.

Comparing with a threshold

The calculator compares the result with a reference value: 0.3 % (EU limit for growing hemp), 0.2 % (former EU limit) or 1 % (Switzerland). Rules for finished products differ from country to country and change often. Some countries look at Δ9-THC, others at total THC. The result is therefore information, not legal advice: check the rules that apply in your country.

Good to know

A certificate is only valid for the batch that was tested. Check that the batch number matches the product, that the analysis is recent and that it comes from an ISO/IEC 17025 accredited lab. Our interactive certificate of analysis guide explains every line.