The short version
If you consume a few times a week, a cartridge almost always costs you less per session than flower. If you go through a gram or more a day, a bulk flower purchase beats carts on price per milligram of THC just about every time. The crossover between those two habits sits closer than most people expect.
This is a math question, not a taste question. Both are sold in the same store, both have price tiers where you can overpay badly, and both get hit with the same taxes at the register.
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Cost per milligram: flower usually wins
Start with what's printed on the label. Flower runs roughly 18% to 30% THC in most US markets. A $40 eighth, which is 3.5 grams, at 22% THC holds about 770 mg of THC. That works out to around 5 cents per milligram.
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Now a cartridge. A 1-gram cart labeled 85% THC holds roughly 850 mg. At $45, that's about 5.3 cents per milligram. Call it a wash on paper. If that same cart is $60 in your state, flower is plainly cheaper.
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Volume widens the gap. An ounce of solid flower at $180 and 20% THC is 5,600 mg for about 3.2 cents per milligram. Carts rarely get a comparable bulk break, and the 2-gram versions are not discounted in proportion.
Cost per session: carts win
Per milligram is not how anyone actually consumes. A joint takes half a gram to a full gram whether you finish it or not. You light it, part of it burns off between puffs, and combustion destroys a share of the cannabinoids before they ever reach you. The THC you paid for is not the THC you absorb.
A cartridge does not burn, and nothing is consumed between sessions. If a typical dose for you is 5 to 10 mg of THC, a $45 gram cart is 85 to 170 sessions, which lands somewhere between 25 and 50 cents each. A single 0.5-gram joint rolled from that $40 eighth costs about $5.70 in flower and delivers one session.
That is the whole argument in two lines. Light and moderate consumers get far more sessions per dollar from a cart. Heavy consumers hit the cart's ceiling fast, and flower's per-milligram advantage takes over.
Where the crossover sits
Rough rule: if a 1-gram cart lasts you longer than about a week, carts are the cheaper habit. If you would burn through it in three or four days, flower is cheaper, assuming you finish what you buy and store it so it does not dry out.
Pick by how you consume
Don't consume much, or consume alone
- Buy one cart, not three. A cart you dislike is $45 gone.
- Ask for the THC percentage before you look at the price. A 75% cart at $35 beats a 90% cart at $55 most of the time.
- Budget $15 to $30 once for a battery, and keep a spare.
A few times a week, usually with other people
- Eighths make sense here because you share the burn rate.
- Skip pre-rolls unless you need the convenience. They are often two to three times the per-gram price of loose flower in the same case.
- Ask the budtender which flower is on special. It rotates, sometimes daily.
Daily, heavy, or gram-a-day habits
- Half-ounces and ounces carry the deepest discount per gram in almost every store.
- A dry herb vaporizer, $60 to $150 up front, cuts combustion loss and lets you dose in small increments. The device cost pays back within a month or two at this volume.
- Check harvest dates. Old flower burns hot and fast, so you go through it quicker than the weight suggests.
Costs people forget
- Taxes hit at the register in most legal states, and rates swing hard from one state to the next. Some add 30% or more on top of the shelf price.
- Clogged or leaking carts waste oil. Store them upright and out of heat.
- Flower you do not finish is not a savings. Buy an ounce to save money and toss a quarter of it, and you paid eighth prices anyway.
- Two stores ten minutes apart can differ by 25% on the identical product. Call ahead or check the online menu before you drive.
Run the math yourself in the store
- Divide the price by grams times 1000 times the THC percentage. That gives you cost per milligram.
- Multiply that by your dose per session in milligrams to get cost per session.
- Do it for the cart and for the flower on the shelf in front of you, then compare those two numbers instead of the sticker prices.
Once you run it with your own tolerance and your own state's tax rate, you will not need anyone else's opinion on this again. The answer shifts with the weekly specials and with how much you actually consume, which is why the picks above are organized by habit rather than by product.