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How to Assess THC and CBD Levels in Cannabis Strains and Products

March 22, 2017

How to Assess THC and CBD Levels in Cannabis Strains and Products

Marijuana buds in the glass plate

How much THC does your favorite cannabis product contain? The answer may not be as straightforward as reading the “total THC” number that is (hopefully) printed on the label. There is no official industry standard for calculating the total THC of a cannabis product, and different producers and testing facilities calculate it in different ways. As a consumer, what you’re really after is the amount of THC or CBD that will be available for your consumption, which will depend on the content of the product, the route of administration, and the method of consumption.

Let’s take a closer look at the different ways you can estimate THC levels in cannabis products (the same logic applies to CBD).

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THCA, THC, and Decarboxylation

If you want to know how potent a cannabis product is, it helps to understand the difference between THCA and THC, and how one gets converted into the other. Cannabis does not make THC, it makes THCA, which is a non-intoxicating compound that can be converted into THC through decarboxylation. This typically occurs in the presence of heat energy applied by the consumer. When your lighter, vaporizer, or oven heats up your cannabis product, THCA gets converted into THC. Many people talk about “activated” vs. “inactive” THC. This is what they mean.

THCA to THC decarboxylation

Figure 1: THC-acid is produced by the cannabis plant. With the application of heat energy, the acidic residue of THCA is removed, producing the psychoactive cannabinoid THC. Cannabis flower normally contains very low levels of THC. The heat applied by consumers converts most of the THCA into THC. (Amy Phung/Leafly)

THCA, THC, and Reading Cannabis Product Labels

Most cannabis products sold legally in the US are required to be tested and labeled for THC and CBD content. However, when you examine a typical label, you’re likely to see several numbers, such as CBDA, CBD, THCA, and THC percentages, and perhaps things like “Total THC” and “Total Cannabinoids.” Let’s look at a real-life example from Washington state:

Figure 2: Example label of a cannabis flower product sold in Washington state (Platinum Cookies by Western Cultured). Notice the numbers listed under “Potency Analysis.” This product contains 23.2% THCA and 1.0% THC by dry weight. “Total THC” represents the total potential THC level of this product—the amount of THC present if all THCA is successfully converted into THC. (Julia Sumpter/Leafly)

Let’s focus on three numbers under the “Potency Analysis” of the above label: THC, THCA, and total THC. On this label, the THC level is 1.0%. Most labels will display a low number like this because the plant contains mostly THCA, which needs to be decarboxylated (“activated”) by heat. In this case, we see 23.2% for the THCA level.

Things get tricky when we look at the “total THC” level, which is 21.35% here. Total THC is supposed to refer to how much THC will be present as a percentage of dry weight after the THCA has been converted into THC. On this example label, “total THC” is 21.35%. But wait, if we have 1.0% THC and 23.2% THCA, why isn’t total THC 24.2%? Shouldn’t we just add the THC and THCA percentage levels together, since THCA will get converted into THC? Nope. There are a couple things that make this tricky.


What Is THCA & What Are the Benefits of This Cannabinoid?

First, THC isn’t quite as heavy as THCA, so we need to account for that. This makes sense if you look at the chemical structures for THCA vs. THC (Figure 1). THC is just THCA after a piece gets chopped off. So, THC is lighter—it’s 87.7% of the molecular weight of THCA. That’s why total THC on the above label is 21.35% instead of 24.1%. When you see something like “Total THC” on a product label, they should be getting that number using a calculation that takes this into account (see Method 2 in Figure 3 below).

Second, the process of turning THCA into THC is not 100% efficient—not every THCA molecule will be converted into a THC molecule, and at very high temperatures, some of the THC may degrade into CBN. Our friends at Steep Hill Labs estimate that 75% is a representative upper limit for what fraction of THCA will end up as THC. In that case, for every four molecules of THCA that get heated during consumption, only three get successfully converted to THC.

While this type of calculation provides a more accurate estimate of final THC levels, in practice it’s very difficult to know what your THCA to THC conversion efficiency will be; it will depend on how long your flower is exposed to heat, the exact heating temperature, and the device you’re using.

Chart of different ways to calculate THC percentage

Figure 3: Three different examples of how people estimate total THC levels. Method 1, which just adds together THCA and THC percentages, is too simplistic and greatly overestimates THC content. Method 2 is the correct way to calculate the maximum potential THC content. Something like Method 3 can be used to account for the fact that not all THCA will end up as consumable THC, but in practice it’s hard make this calculation. The 0.75 value is what Steep Hill labs uses, but the exact number will depend on several other factors. (Amy Phung/Leafly)

Final THC Levels Depend on Consumption Method

“Heating of cannabis extracts at 200°C for five minute results in almost 100% decarboxylation of THCA to THC, without forming CBN.”
Dr. Rudolf Brenneisen, University of Bern, Switzerland

To better understand how different consumption methods affect decarboxylation rates and the final THC content in cannabis products, Leafly spoke with Rudolf Brenneisen, PhD. His lab at the University of Bern, in Switzerland, has extensively studied how decarboxylation rates and THC availability are influenced by different products (specifically, vaporizers) and routes of administration.

Dr. Brenneisen emphasized that “Decarboxylation efficiency/rate depends on heating temperature and time, as well as the vaporizer design and technology.” His lab has specifically studied how different vaporization temperatures and products affect how efficiently THCA is converted into THC in both flower and cannabis extracts. “Heating of cannabis extracts at 200°C for five minute results in almost 100% decarboxylation of THCA to THC, without forming CBN,” he said.


What is decarboxylation, and why does your cannabis need it?

Decarboxylation of THCA to THC starts occurring at around 180°C. As you increase the temperature from there, other compounds like terpenes will begin to vaporize, each at a different temperature. At even higher temperatures, you’ll start to get combustion. This will affect not only levels of THC and other cannabinoids, but also terpenes. Moreover, combustion can produce byproducts that may be hazardous to your health.

“Burning of cannabis (not tested and validated in my lab) at >700°C will probably result in a higher decarboxylation rate, but also more degradation to CBN and the production of potentially harmful byproducts.  In addition, temperatures that are too high lead to loss of terpenes, which are important ‘entourage effect’ compounds,” Dr. Brenneisen explained.

Differences between vape vs. combustion temperatures on THC

Figure 4: Different consumption methods will influence the cannabinoid and terpene levels that consumers ingest. Vaporization occurs at lower temperatures than combustion, and is less likely to cause further breakdown of THC into CBN or destroy terpenes. However, the cannabinoid and terpene content of vapor will vary with different vaporization temperatures. (Amy Phung/Leafly)


There isn’t an exact, magic number for the temperature at which cannabis flower starts to combust, but the temperature range of most commercial electric vaporizers should be below this threshold. Traditional smoking methods that directly ignite flower are a different story. The temperature of a typical Bic lighter flame will be well over 1,000°C, which would be expected to cause degradation of THC into CBN and some destruction of terpenes. These factors will naturally influence the nature of your experience.

The Takeaway

You want to know the theoretical maximum percent dry weight value for the THC content of your product. The same logic applies to CBD. If the product is labeled well, this value should appear as “total THC” or something similar, and should be calculated as follows:

Total Potential THC = (0.877 * %THCA) + %THC

This is the theoretical maximum amount of THC present in your product. It accounts for the weight difference between THCA and THC, and assumes 100% conversion of THCA into THC. But the conversion efficiency may not be 100%, which is why this is a maximum estimate. The real amount of THC available for your consumption will probably be lower than this number. Estimating exactly how much lower is tricky because, as we explored, it depends on the details of your consumption method. And of course, all of this depends on having a cannabis product that has been honestly and accurately measured. It’s entirely possible that certain cannabis products on the market today have not been accurately tested, and the numbers on the label may be inflated. If you’re new to cannabis, be sure to ask a budtender to recommend quality products from trusted sources.

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Dussy FE, Hamberg C, Luginbühl M, Schwerzmann T, Briellmann TA. Isolation of Delta9-THCA-A from hemp and analytical aspects concerning the determination of Delta9-THC in cannabis products. Forensic Sci Int. 2005;149(1):3-10.
Elzinga S, Ortiz O, Raber JC. The Conversion and Transfer of Cannabinoids from Cannabis to Smoke Stream in Cigarettes. Nat Prod Chem Res. 2015;3(1). PDF
Lanz C, Mattsson J, Soydaner U, Brenneisen R. Medicinal Cannabis: In Vitro Validation of Vaporizers for the Smoke-Free Inhalation of Cannabis. PLoS ONE. 2016;11(1):e0147286. PDF

Nick Jikomes's Bio Image

Nick Jikomes

Nick is Leafly's principal research scientist and holds a PhD in neuroscience from Harvard University and a B.S. in genetics from the University of Wisconsin-Madison. He has been a professional cannabis researcher and data scientist since 2016.

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  • This is a good article but contains several details that need clarification. First, for reference, 180’C is 356’F. Decarboxylation will start around 100’C (212’F). However this will take longer and be less efficient than Dr. Brenneisen’s method. Importantly, though, at 180’C (356’F) you get vaporization of THC, CBD, and many terpenes. You would not want to decarboxylate at that temperature as you will lose all the medicinal components, unless you’re vaporizing at the same time. So, to decarboxylate for edibles etc, you want lower and slower temperature to retain the medicine. If you put your flower into a good vaporizer then 356’F is the magic number that both decarboxylates and vaporizes the THC etc. Also, recent study showed that a good vaporizer (they used a Storz-Bickel Crafty) achieved 80% decarboxylation.

    • Ron Nahmod

      ar3 u answering questions?

    • Jackie Meyer

      How low and how slow? This is for migraines and fibromyalgia, so I want to make sure to keep the cbd

      • There are many protocols for decarboxylation, some better than others, but the one I use which is very memorable is 100 for 100. This means 100’C (212’F) for 100 minutes. I can’t vouch for the efficiency of this, but it won’t lose the cannabinoids or terpenes.

    • Alexander Luft

      You have convinced me to start vaping. Signed, retired physician.

  • Stewart Hughes

    I wonder if there are other plants with the same potential,,,

    i didnt get the purpose of this article,,

  • The ratio of THC to CBD is what the United Nations – and their single convention on drug control – as the recommended method for distinguishing drug type from fiber type cannabis. It was subsequently discovered that CBC – cannabichromene had been misidentified as CBD. The ratio of THC to CBD had no business in forensics and is a useless ratio when chooosing a strain for medicinal purposes. What would be very useful is a strain fingerprint – including all the cannabinoids and terpenes present in every strain being sold. Many Indica dominant strains contain very little CBD relative to CBC, CBG and THCV.

    • jwinks

      My question and thoughts exactly. In dispensaries are they more specific? Or is that a waste of time and money ?

  • Vol Hawk

    I’ve read one recommendation for turning THCA into THC … which is basically to heat THCA for 5 minutes at 200 degrees C.
    But… Jordan Tishler is saying that CBD and THC vaporise at 180 degrees C.
    Perhaps this is because the decarboxylation occurs when THCA is gaseous.
    Is that correct ?

    I’ve also read that to convert CBDA to CBD we should heat up the cannabis to 230 degrees C for up to 30 minutes.
    But again… is it, or is it not true, that CBD and THC vaporises at 180 degrees C ?
    It took me years and years to stop smoking cigarettes. For this reason i prefer edibles.

    My question is: At what temperature should i cook my bud and for how long ?
    (in oil/butter, or in chocolate, or ground and sprinkled into cakes / cookies)

    I will be very grateful to anyone offering answers to this question
    Thanks for your help…. Have a nice day . 🙂

    Vol Hawk

    • Sorry I didn’t see this sooner. There are several issues embedded in your question. One is decarboxylation which I give a recipe for above. The other is extraction into oil/butter etc, which is a different question. As I recall, the more you cook it the more you extract. However, at some point there are diminishing returns. 30-40 minutes on low heat will do fine. You will lose the terpenes but that’s true for all edibles unless you do a cold extraction (in ethanol, for example).

      • JwalaB

        It seems you might not have an answer to my questions and some of your answers are based on what you remember but. Your knowledge seems sound so I will ask anyway.

        I have a few questions I suppose. All started by my looking for the best cbd cartridge available for vaping.

        ( I came back up here after realizing it’s annoying and I can’t form a question because the world if these products is just trash. People touting the highest blah blah blah. But 10% if that have a damn clue what they are really doing.
        A succinct question I have is- I saw a cannibinoids test once and it said 20% thc by weight. 97% by distribution.
        What the hell does that mean? What is by distribution??? That makes no sense to me. And I can’t find any scientific documents in something by weight and by distribution )

        So. My problem is that. There’s lots of people making stuff and companies that are just copying a process. But they have no real idea what they are doing. They say all sorts of things like their product is 100% pure. It’s hemp derived this. Something derived that. And then there isn’t the ratio nonsense. 1:10. Which in the end… seems to honestly tell you nothing about how much cannibinoids are there. It could be 10mg:100mg total. 50mg And 500mg. Etc.

        But. What I’m finding is that most carteidges are not explaining much. First I want a cartridge that is not pure cbd isolate. Because multiple studies are finding that the so called spectrum is better. That is to say that. Some amount. Even if minimal. Of Cbn. Cbg. CBC. And thc. Is beneficial. Much more that 99% pure cbd alone. Which has a bell curve distribution of effectiveness as dose increases.

        But when someone has a cartridge that is 20:1 cbd and 10:cbd and 1:1.

        What the hell is going on?
        Are they making some sort of oil. And then back adding cbd isolate to reach desired ratios???

        There are the cbd high strains. AC/DC charlottes web. That may have something like 1%thc:20%cbd by weight.
        And hemp which could have a ratio of cbd to thc that is around 1:10 or 1:5.

        But. None of them say flower derived cbd oil. Some say hemp derived but. No way the My are using multiple strain specific henps that natirally have those ratios so that the ratios are then present in the (usually co2) extracted oils.

        At first I was trying to find a healthy oil due to many oils at the beginning being butane type concentrates. Wax and shatter. That people were thinning with pg and glycerol and such like ‘vape juice’ is made. Which is crap.

        But from what I’ve been reading. Co2 extraction seems to produce an oil thin enough to be vaporized in a cartridge.

        Still the question remains as to what all this stuff is. It’s just. It’s really annoying. You look at any of the carteidges and they don’t make any sense. They are all using random ass science and it’s. Ugh. I can’t even form a question for you coherently because what do I freaking ask. I’m sure you don’t know the best cbd cartridge brand.

        And when you google that you get HORRID responses. Mint flavored. Glycerin. Vape juice. That has 30mg of cbd from god knows where. In some bs…. just. I don’t know.

        I want a full spectrum. Derived from high cbd marijuana plants. Cartridge. Maybe hemp could do but. I can’t find any science on what the normal % are for a co2 extraction of hemp.

        Ugh. Just. Pure. Ugh. Tell the fucking patients what your deriving it from. The extraction method used. The %s. Just. Fuck

  • Sunny

    I only wanted to know how to tell how much cbds are in these oils and stuff I’m buying. Is there a test that can be done . or can they claim there is 500mg of cbds and how can i verify it.

    • Ron Nahmod

      me too to see if cbd or thc oil

    • Joy Ogozelec

      There isn’t a way for you to do it without a lab. The most important thingt to keep in mind when you buy CBD products is to find a reputable company. Since CBD doesn’t cause any obvious effects, except feeling better once you’ve found your therapeutic dose, it can be easy to buy a snake oil product. Also, avoid products derived Chinese hemp.

    • Juju

      There , are, at home testing kits on google.

  • Ron Nahmod

    how to home test if thc oil or cbd in vape

  • Fred

    Quick question. So to get the best thc and cbd levels, one should first decarboxylate, then smoke or vape

    • Sam Moorman

      From above. From the smart guy. So, to decarboxylate for edibles etc, you want lower and slower temperature to retain the medicine. If you put your flower into a good vaporizer then 356’F is the magic number that both decarboxylates and vaporizes the THC etc. Also, recent study showed that a good vaporizer (they used a Storz-Bickel Crafty) achieved 80% decarboxylation.