OH’s Law Of Cannabis Edible Potency

OH’s Law Of Cannabis Edible Potency

People have been asking me quite a bit lately “How the ^%#@! do I figure out the potency of home-made capsules or edibles?” So I thought I’d sit down (after one of my own capsules kicked in) and write it up once and for all.

Yes, the title is a play on “Ohm’s Law”, and just like Ohm’s Law, the real power is in knowing which form of the formula to use. So I’ve written up some examples. And even though I think I have a good handle on my ego, I still have enough of one that I’d like to get credit for working this out. So here you go, world.

G = grams of cannabis
P = potency in milligrams of THC
S = strength of cannabis in percent
N = number of servings

For the S factor, you simply read the strength off the label if it’s legit stuff from a dispensary. Otherwise, assume 20% for top shelf/fire buds, 10% to 15% for mids/reggie, and 5% for schwag/brickweed.

For concentrates, assume 30% for kief, 40% for hash, 60% for hash oil, 80% for shatter.

What Potency Will My Edibles Be?

What potency will my edibles be if I start with G grams of S strength and I want N servings?


P = \frac {10 (G * S)} N


For instance, let’s say you have an eighth ounce of Really Good Weed that’s 20% THC and you want to make 16 brownies. How strong will each of them be?

An eighth ounce is 3.5 grams, so it’s

10 * (3.5 * 20) / 16 = 700 / 16 = 43.75 mg each

Notice that the amount of oil, butter, alcohol, or whatever you use has nothing to do with the calculation! So if you’re making enough cannabutter or canna-coconut oil for a batch of brownies, you use the amount your recipe calls for 16 brownies, and that’s all there is to it.

Also, if you’re trying to calculate CBD or any other cannabinoid, it’s the same formula, you just have to know what the percentage of CBD is, which is always given as a percentage by weight.

How Many Servings Will I Get?

How many servings will I get if I start with G grams of S strength and I want P potency?


N = \frac {10 (G * S)} P


Example: You just bought a quarter ounce of mids and you’re looking to make some fairly light capsules with 5 milligrams of THC each. How many can you make? A quarter ounce is 7 grams, and we can estimate that “mids” are about 10% THC, so:

10 * (7 * 10) / 5 = 700 / 5 = 140

You’d end up with 140 capsules. Now, to figure out how much coconut oil you’d need, let’s say you’ll be using #00 capsules, which hold 0.95 ml each. 140 * 0.95 = 133 ml, or just about 9 tablespoons.

How Many Grams of Cannabis Will I Need?

How many grams of cannabis will you need to make N servings of P potency, if the cannabis is S strength?


G = \frac {N * P}{10S}


Example: you want to make 24 brownies with a solid 75 mg THC in each, but all you have is schwag. How much of this schwag are you going to have to stuff into your butter?

Let’s be generous and say schwag is 5% THC, so:

24 * 75 / 10 * 5 = 1800 / 50 = 36 grams, or enough to get you in real trouble in most states where you are limited to buying schwag.

And, just to be complete:


S = \frac {N * P}{10G}


This form tells you “how strong of a strain do I need if I am starting with G grams and want N servings of P potency each?” Not generally useful or practical, but there you go.

Credit Where Credit Is Due

Please credit “Old Hippie of BeyondChronic.com”, and link to this article instead of republishing it as your own work!

About Old Hippie

http://gplus.to/OldHippie Old Hippie is a father of two boys and thankfully living in California where all this kind of thing is legal. He started smoking marijuana in 1967 in high school, experimented with mind-expanding drugs of all kinds, and then straightened out 15 or so years later to become an airplane pilot. After being diagnosed with depression in 2000, he lost his job and most of the following decade to prescription medications (such as antidepressants) which sapped his energy and will. Finally, a chance conversation with a friend led to a doctor’s recommendation for medical marijuana (MMJ). This changed his entire life, health, and outlook for the better. BeyondChronic.com is his continuing story. It’s also his way to provide experienced advice on using medical marijuana effectively and responsibly, as well as advocacy, activism, and support for others. Old Hippie teaches about safe use of cannabis edibles, Canna Caps, vaporizers, dosing, and even microdosing.


Honestly, I just sat down and worked it out, the trickiest part was getting the units into the formula. Maybe I can get Felicity to read this comment and she’ll appreciate me a bit more. Thank you! Nugs and hugs!

Can you help me with the math? I had my oil tested, but I have no idea how to figure out how to do the math.
So lab test is as follow. 3mg/ml total THC.
I would like to know how much is in an ounce. Your help would be greatly appreciated.

Always happy to! Don’t worry about the math, just think carefully and use common sense and you’ll figure it all out. Nugs and hugs!

YOU are incredible!! I have read your information in blogs it’s reassuring ~I have used opiates as needed they were heavy very difficult coming off those I live in Oregon so thankful for that! Medically I am a mess the real problem I was diagnosed with PTSD in 1986 so it’s difficult to understand recipes etc. My disability when I was assaulted my pay so like others on SS. I think I am going to purchase ” Magic Butter Machine” I would like to get to making capsules after all I was taking 3 a day 10 mg. First I cut them in half 2.5 years later they weren’t working I knew better too, seen many people messed up as I used to be in law enforcement, corrections ~ never lied or harassed I was one of the good ones I Promise to you 🙂 I deal with chronic depression, Rheumatoid arthritis, and the pain has made me isolated. I went into a dispensary purchased THC 0.85 & CBD 13.76 I made a pan of brownies ~ I could stand and cook! I wanted to interact with people it made me feel like I was 15 years younger man oh man!! It was so cool to be able to be ” BACK” Life is still hear 🙂 Bless you Old Hippie Thank You

Wow, such great news!!! I am so happy for you! Now as you get used to this, try some slightly higher THC strains if you can, because THC is definitely a boon for both depression and arthritis, but don’t overwhelm yourself. Remember, virtually all problems with cannabis occur from simply taking too much! Nugs and hugs!

OH, I’m a little confused here. Maybe I just don’t understand fully. In all of these equations there’s an extra division step. What is the purpose of this division?

What the equations do is take care of all the semi-complex values in milligrams and percentages. There’s just one division step though, so I’m not quite sure what you’re referring to.

This equation isn’t complete.

You’re missing decarboxylation efficiency. Generally unless you have access to a lab grade oven you’re going to decarb at best around an 88% efficiency (I calculated this based on the results of the 2015 Karma Cup and amateurs should expect a lower efficiency). A 70% efficiency would be a more accurate gauge for an amateur decarbing for the first time.

These numbers are also considering that the end user is eating the starting material. If they’re infusing and straining out plant material then they should expect considerably lower numbers.

You have some good points here, and we could debate the fine points of this all night. I’m just trying to keep it simple and understandable. There’s only about 70% efficiency when you inhale smoke as well, but that’s only important if you’re actually doing medical research. The important thing is to give people a reasonable ballpark estimate of what’s going on, and frankly I’d rather they erred on the low side of dosage.

Hi, I’m after some advice on how much cannabis I should use to make cannabutter to make into scones to help my grandma with the difficulties she facing with her cancer such as pain, nausea and discomfort. She’s not managing to eat very much at the moment so I wanted to make some small scones that she could just have half of and then if she wants to have more she can. I only need 21g of butter for the scone recipe I have but have no idea how much cannabis needs to be used in order to get her dosage not too high. Any advice would be amazing, we have got high quality cannabis available so I don’t want them to be too strong for her so that it puts her off trying it again. We want to make about 10 scones to begin with and see how she gets on before we make any more. Thank you 🙂

First of all, my traditional salute: Fuck Cancer!

OK, let’s do this. We’re looking at the third version of the formula (How Many Grams of Cannabis Will I Need?):

N = 10 because your recipe makes 10 scones
P = 5 because 5 mg of THC is a very low and safe place to start
S = 20 because without lab-tested medical cannabis, 20% is about the strongest street stuff available

So 10 * 5 = 50 / 10 * 20 = 200. 50/200 = 1/4, so only 1/4 gram necessary.

Thank you so much! I had thought that’s all we needed but it sounded like too little an amount. If I want to make 100g of butter instead of 21g that I need for the scones do I need to add 1 1/4g? I want to make extra butter so that if she gets on with the scones I can make her something else. Am I better to wait and see if she’s okay with the dosage so I can adjust the amount of cannabis I use? Thank you so much for your advice

Also, do you know of a good canna butter recipe that I can follow? I’m new to cooking with cannabis and don’t want to mess it up. All the ones I’ve found say to use 500g of butter and 28g of decarbed cannabis but that sounds like too much.

Yes, please wait! It’s possible to adjust the dosage of the butter afterwards, but it’s always better to know more about the patient before you commit to a plan, if possible. I love the idea of medicated scones, it’s so British, but that’s still a lot to eat if you have no appetite!

Hi Old Hippie,

After much searching I really appreciate finding your site and work. I was wondering if you are able to help decipher lab tests, if I were to send you a recent lab test for a cannabis oil. Would love to get your feedback in reading it if you have the time. We are trying to figure out dosing for my brother who is self treating a goiter and don’t want to overdo it. Thanks in advance.

Greetings from another aging hippie. I wanted to stop and thank you for working out the formulas. This is a fine resource you’ve shared with us. We’re making good use of it on another site. The poster did indeed give you full credit and linked us to your site. Bang-up job. My members and their loved ones thank you also.

How much herb would I need to make 100 ’00’ capsules using cannabutter made with coconut oil. I want the doses to be strong

The formulas work perfectly for both flower and concentrate, because the weight and potency are both factors. You can use the formulas (or just a simple calculation), for instance, to show that a typical gram of concentrate is approximately equivalent to a typical eighth ounce of flower.

Dear Old Hippie!! Thanks for this!! This is all great info! Much appreciated.

Point of clarity…Hopefully you can help me out….I get confused a bit with the calculation when it comes to making capsules at a certain ‘P’ (potency). Especially after reading, ‘Notice that the amount of oil, butter, alcohol, or whatever you use has nothing to do with the calculation!’

I’m trying to calculate number of grams ‘G’ I need to use in order to get the desired ‘P’. But if the amount of oil or butter doesn’t matter than what do I use for ‘N’ in calculating the amount of ‘G’ I need?

For Example:

G: How many grams of flower needed?
P: Target is 15mg/capsule
S: Potency of Flower is 13%
N: How or what do I use for ‘N’ to calculate ‘G’?

Do you see where I get a little confused?

I guess I’m asking the same type of question ‘Dalex’ was asking…

Look forward to hearing back from you!! Thanks again!!

My dear friend…you are simply confusing yourself by attempting to solve two problems in one equation. That’s because the amount of oil really has nothing to do with the potency, but it DOES matter when making capsules! You’re trying to make some very strong capsules, so I’ll assume #00 size capsules here, which have a capacity of 0.95 ml each (as noted in the Canna Caps article).

And here’s where the confusion comes in, because without knowing how many capsules you want, how can you possibly figure out how much cannabis, or even oil, you need? You can’t. So let’s assume 50, which is a fairly standard number. 50 * 0.95 is just short of 48 ml and a bit over 3 tablespoons of coconut oil. Now plug the 50 (N for 50 capsules) into the formula and you get 50 * 15 / 10 * 13 = 5.75 grams or so of cannabis needed. Nugs and hugs!

I still have no idea lol I am totally crap at math and this just makes it worse for me but you do a fantastic job on this site so Thanks 🙂 Plus it is really hard here in Australia to figure out any of this as we have no legal way of getting our herbs so until I can get my own growing again I don’t think there will be any point in trying to estimate what’s in my tinctures using my new MB2, not that I have got to make any yet still waiting to get a supply of herb to try it out 🙁 Plus I am still trying to decide on how to do it with my MB2 it will either be the Green diet website way ( no decarboxylating ) or the way you do it here on this website ( still studying) sorry for the long winded comment this is my first post here 😀 Anyway I suffer from chronic pain from a spinal injury and just want to make the strongest tincture/oil I can from the not so good herbs we get in Aus using my MB2 without having to boil it down afterwards to strengthen it anyway I am sure I have much much more to learn so better get reading on your site and once again Thank You for such a great resource I had no idea how to proceed until I saw your site and Green Diet which is how I found your site via a link 😉

Thanks, mate! I’m going to have to check out this Green Diet site and see why they recommend not decarbing, but if you want it strong you certainly should decarb! And it’s actually typical to boil away excess alcohol to suit it to your taste/strength, so don’t be too turned off by that.

P.S. If you don’t like math or have problems with formulas, check out this site one of my Reddit buddies came up with: http://www.howtoedibles.com/

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