How many grams are in an eighth of weed?

3.5 grams. US shops round an ounce to 28 grams, so an eighth is 28 ÷ 8 = 3.5 g.

How many grams are in an ounce of weed?

28 grams on dispensary menus. A science ounce is 28.35 g; BudMath uses the 28 g retail ounce shops actually sell.

How do I compare two cannabis prices?

Divide each price by its weight in grams. The lower dollars per gram is the better buy. BudMath Compare does that for eighths, quarters, ounces, and other retail units.

BudMath is a free cannabis calculator for eighths, ounces, and price per gram. Enable JavaScript to run the math.

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About BudMath

Free cannabis calculator. Split leftover ounces into eighths and prerolls, convert 28 g ounces, compare price per gram, and see how long a buy lasts. No account.

Math stays on this device. We only count which tool you used — not the numbers you typed.

The 28 g ounce

Flower is weighed in grams, but people still buy “an eighth” or “an ounce.” US shops round 1 oz = 28 g (not the science 28.35). Easy map:

eighth 3.5 g · quarter 7 g · half 14 g · ounce 28 g

What to tap

Breakdown — pick a bag size (eighth, quarter, half, oz). Combos fill that size first, then split whatever is left into smaller bags and prerolls. Each row is an alternative, not a stack. Drag the tape to set the weight.
Convert — same pile, different name. Eight eighths is one ounce.
Compare — two prices, same $/g. Add the THC % on the jar for a theoretical $/mg from the label, not a dose.
Lasts — days left at your daily grams, from the total you paid.

Common questions

How many grams are in an eighth of weed?: 3.5 grams. US shops round an ounce to 28 grams, so an eighth is 28 ÷ 8 = 3.5 g.
How many grams are in an ounce of weed?: 28 grams on dispensary menus. A science ounce is 28.35 g; BudMath uses the 28 g retail ounce shops actually sell.
How do I compare two cannabis prices?: Divide each price by its weight in grams. The lower dollars per gram is the better buy. BudMath Compare does that for eighths, quarters, ounces, and other retail units.
Is BudMath free?: Yes. No account. Math stays on this device. We only count which tool you used, not the numbers you typed.

What it won’t do

No menus, deals, or “low / mid / high” potency guesses. Label THC is jar math, not how much you absorb. Estimates only — not medical or legal advice.