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Understanding and Correctly Interpreting THC/CBD Levels in Cannabis

Tetrahydrocannabinol or THC is the main psychoactive compound responsible for the euphoric ‘high’ that you feel after consuming cannabis, so it pays to know how much ‘content’ is in your favourite strain.  

The answer to this, however, is often not as simple as taking a look at the ‘Total THC’ number on the label. Furthermore, an industry benchmark for calculating total THC or CBD (the non-psychoactive compound) has not been established as yet, and as such, producers and lab facilities calculate cannabinoids in their own unique way.  

As a cannabis consumer, you should be familiar with what percentage of cannabinoids is present in your product, namely the amount of THC or CBD that’s available for consumption. How much is available largely depends on the main ingredients of the product and how you will consume it – vape, dab, tincture, smoke, etc. 

In this article, we discuss various ways through which you can get an accurate estimate on the amount of THC present in your product – the exact same logic applies when determining CBD levels.  

The Relationship between THCA, THC and ‘Decarbing’   

To determine the potency of any particular kind of cannabis product, we need to first understand the key differences between raw THC in its acidic form – that’s THCA – and decarboxylated THCA, which is classified as the ‘psychoactive THC’. We, therefore, need to understand how the former gets converted into the latter.  

Cannabis does not make THC on its own – in its raw form, it has THCA – a non-psychoactive compound which can only be converted to THC via decarboxylation.  

How to Make Heads and Tails of Cannabis Labels 

Unfortunately, majority of cannabis products sold do not have a clear label saying, for example, that if there’s 23% THC then 23% is what you’ll be getting.  

Legal marijuana products sold in the US are required under law to be lab-tested and labelled for both THC and CBD. However, it often isn’t as straightforward as that – upon close examination, you’ll see other numbers as well, such as THCA, CBDA and percentages for ‘Total THC’ and/or “Total Cannabinoids’.  

To give you a real-world example, let’s take a product label that focuses primarily on 3 numbers: THCA, THC and Total THC. Let’s say the THC level on the label is 1% – it should be noted that majority of labels will display a low value for this because in all likelihood the plant will contain mostly THCA, which needs to be activated or ‘decarbed’ via heat. In this case, we shall assume the corresponding THCA value to be 23%.  

Upon examining the Total THC percentage, we see that it’s 21.35%. Total THC generally refers to the amount of ‘dry weight THC’ that’s available after THCA has been converted to THC. So, if our label indicates 21.35% to be Total THC, we will probably be left bewildered because:  

If it says THC is 1% and THCA is 23.2%, then why isn’t the collective Total THC level indicated as 24.2%? As common sense would dictate, can’t we just add the THC and THCA percentages to determine Total THC, since the THC was converted from the 23.2% THCA? Well, not quite – it’s not that simple, as much as we’d like it to be.  

Reading Labels ‘Correctly’      

Time to take a step back – first of all, THC is not nearly as ‘heavy’ as THCA, so that must be accounted for. If you ever get a chance to look at their chemical structures – something which we could dedicate an entire article to – you’ll see that THC is simply THCA, but with the acidic component chopped off.  

Therefore, THC is lighter – to be precise, it is 87.7% lighter compared to the molecular weight of THCA. This explains why Total THC on the above product example is actually 21.35% and not 24.1%. So the next time you come across ‘Total THC’ on a cannabis product label, understand that it’s based on a calculation that takes all of this into account. This is something we’ll be elaborating on shortly.  

Secondly, the decarbing process which converts THCA into THC isn’t 100% efficient – so what we’re saying is that not every single one of the THCA molecules will convert seamlessly into a THC molecule. In fact, in some cases where temperatures are really high during decarboxylation, some of that THC may get downgraded to CBN.  

Many cannabis labs have estimated that 75% is a good representation of the upper limit for what percentage of THCA will likely get converted to THC. This would mean that for every four molecules from each gram of THCA that gets heated during the decarbing process, three will get converted to THC.  

Bear in mind that, on one hand, this kind of calculation can yield accurate estimates for Total THC level, on the other, it can be tough to know exactly how efficient your THCA-THC conversion was; because there are multiple factors that come into play such as the amount of time the bud was exposed to heat, the heating temperature and the device which was used.  

Here are 3 examples of how professional lab testers typically determine Total THC levels: 

Method #1 

Add the THCA percentage to THC percentage – being the simplest method, it is often not as accurate as the other two and can greatly overestimate THC levels.  

Method #2 

Multiply 0.877 with THCA percentage; add this value to THC percentage – this method attempts to account for the difference between THCA and THC in terms of weight. It is relatively simple and yields slightly more accurate results, but calculates only the total ‘potential’ THC level.  

Method #3 

Multiply 0.75 with 0.877 and THCA percentage; add the value to THC percentage – this method can be complex but yields the most accurate result. It accounts for the ‘imperfect’ conversion of THCA to THC and is a reliable method for estimating Total ‘available’ THC.  

As we can see from these 3 methods, an estimate can be had on the Total THC value. To reiterate, the first method simply adds up the THC and THCA percentages, which is not only simplistic in nature but also overestimates THC content by a noticeably wide margin. The second method is a proper way of calculating maximum potential THC content that’s available.  

Finally, the third method realistically demonstrates that not all THCA will successfully be converted to consumable THC – however, in actual practice, it can be complex to make this calculation. The 0.75 value that you see is what’s used by most well-established cannabis testing labs – however, the exact value depends on a variety of factors, one of which is the mode or method of consumption. 

‘Available’ THC Depends on Method of Consumption 

Part of understanding available THC levels in a cannabis product revolves around the fact that a variety of consumption methods and administration routes can affect decarbing rates, and in turn, this will directly influence the total THC content. 

Decarbing rate or efficiency depends not only on factors like time and heating temperature but also vaporizer build and/or technology. Different vaporization temperatures as well as vaporizer designs have a direct impact on how effectively THCA gets converted to THC in cannabis flowers and extracts; 

For example, when cannabis extracts are heated for 5 minutes at 200°C, nearly all of the THCA is successfully converted to THC, without the possibility of any CBN by-products. 

THCA-THC decarbing starts at approximately 180°C. If the temperature is increased, other compounds such as terpenes will also vaporize, at their own respective temperature points. At higher temperatures, however, you get combustion. This can affect not just THC levels and other cannabinoids in the strain, but also terpenes.  

The key thing to understand here is that there isn’t any universal benchmarking number for temperatures at which flowers start to combust – however the ‘temp range’ for majority of electric vaping devices needs to be well below 700°C. So if you’re thinking of achieving decarbing at a faster rate to see better THCA to THC conversion, by way of increasing heating temperature, think twice.  

You might end up with combustion which will not only lead to degradation and formation of CBN, but also loss of terpenes and the introduction of certain by-products – all of which will eliminate the euphoric ‘entourage effect’ of cannabis.  

Key Takeaway 

At the end of the day, what you’re after is the theoretical maximum dry weight percent value for THC content in your product. The very same logic goes for CBD. A properly labelled product will always show this as Total THC which should be calculated this way: 

0.877 x THCA% + THC% = Total Potential THC 

This is the theoretic maximum available THC in your product – it accounts for the weight difference between THCA and THC, assuming that all of the THCA has converted to THC. The actual THC available for consumption will be slightly lower than this number.  

Not all cannabis products are accurately or honestly labelled.  

For this reason, we always recommend buying quality products from trusted and reliable sources only.  

We have detailed characteristics on all our strains on Seedsman.


Cultivation information, and media is given for those of our clients who live in countries where cannabis cultivation is decriminalised or legal, or to those that operate within a licensed model. We encourage all readers to be aware of their local laws and to ensure they do not break them.