how many grams in a cup of peanut butter, depending on the jar in your cupboard

Say it’s the night before a school fundraiser and there are two jars of peanut butter on the counter. One is a smooth supermarket brand. The other is a natural jar with a slick of oil on top, and it’s half empty. The recipe wants one cup, and you’re wondering whether it matters which jar goes in.

Short version: how many grams in a cup of peanut butter is about 258, going by USDA, with King Arthur a bit higher at 270. It does matter which jar, a little. Smooth and stirred is what the number assumes. Everything else needs a small adjustment, and this is how to make it.

The smooth jar, which is the baseline

ExactCups answers how many grams in a cup of peanut butter with 258 g, or 9.1 oz. That comes from USDA’s record for smooth peanut butter without salt, FDC 172470. Half a cup is 129 g, a quarter cup is 64.5 g, and a tablespoon is 16.1 g. A teaspoon comes to 5.4 g, which is small but real.

King Arthur Baking lists 135 g for half a cup, so 270 g for a whole one. The two sources sit about 4.5 percent apart, just inside the 5 percent tolerance the site allows for fats. That’s why confidence is marked medium until a third independent source turns up.

The natural jar with the oil on top

Why stirring matters

Natural peanut butter, just ground peanuts and salt with no added palm oil or emulsifier, separates on standing. The oil floats up and the solids sink. The 258 g figure assumes you’ve stirred it into one even mass, so the jar on your counter needs a proper stir before anything gets measured.

What goes wrong if you skip it

Say you scoop from the top of a half empty jar, all oil and very little paste. Then scoop the last bit from the bottom, all paste. Neither cup is likely to land on 258 g. A good stir fixes it before you start.

Crunchy and reduced fat

Chunky and crunchy jars are kept as separate products on the site. USDA’s record for chunk style, FDC 172473, lists 258 g a cup, the same as smooth. Even so, peanut pieces make a cup less repeatable from one scoop to the next, so ExactCups says it deserves its own entry with its own sourcing.

Reduced fat is another story. Those jars usually add maltodextrin and other bulking agents, which raise the density, and the 258 g figure doesn’t cover them. If your label says reduced fat, treat the number as a starting guess and trust the scale more than the cup.

A fundraiser worked out in grams

Back to the fundraiser. Say the recipe needs two cups of peanut butter for a double batch. On the smooth jar’s numbers that’s 516 g. Put the bowl on the scale, zero it, and pour in the stirred natural jar until it’s empty, then top up from the smooth one until the display reads 516. Nobody has to wrestle two measuring cups.

That’s the whole argument for weighing. Jars of different brands and styles don’t have cup lines printed on them, so a cup is really a guess at how hard someone pressed. A gram is a gram, whichever jar it came out of.

Smaller and larger amounts

Three quarters of a cup is 193.5 g and two thirds is 172 g. A third is 86 g. For a recipe that wants a hundred grams, you’re at about 0.39 of a cup, a touch over a third. Quarter cup and tablespoon figures are further up if you need them, and nothing here is hard to scale by hand.

Ounces catch people out. A weight ounce is 28.3 g, so 8 oz is 226.8 g, only 0.88 of a cup of peanut butter. A full pound, 453.6 g, is about 1.76 cups. A cup of peanut butter outweighs a cup of butter, which is 227 g, by about 31 g.

What the labels say, and why that’s only a hint

The big smooth brands, Jif and Skippy included, declare 32 g for 2 tablespoons on the label. That’s 16 g a spoon, which matches the USDA portion to the nearest gram. Labels round on a small measure, so they’re too coarse to count as measurements, but the match is a nice nudge towards the USDA figure.

From that the site reads King Arthur’s 270 g as a more forcefully packed cup. Nobody’s cheating there. A jar has no cup lines, so the cup weight depends on how the person measuring pressed the paste in, and that’s the whole reason two good sources can sit a few percent apart.

Why it lands in the fat category

ExactCups files peanut butter with butter and the oils, even though it’s only roughly 50 percent oil by weight. The reason is how it behaves in a cup. It’s a plastic solid at room temperature that deforms under pressure and doesn’t compact much as you fill, so it acts more like a fat than like a powder.

Butter has one big edge on it. US butter is sold in cup marked wrappers, so its cup weight is set by the packaging and every source agrees within half a percent. Peanut butter has nothing like that. No standards body publishes a bulk density for it either, and the FDA’s rule only says it must be at least 90 percent peanuts.

Checking the page for yourself

The page was last checked in mid September 2026, and it names both sources behind the number, USDA and King Arthur. Two independent sources agree, which is enough to publish, but the site keeps confidence at medium. If a third measurement ever lands, the figure might shift by a gram or two.

A quick walk through the spoon method

No scale at all? Count tablespoons. A cup holds 16 of them, and a tablespoon of peanut butter is about 16.1 g, which brings you back to roughly 258 g. Level each spoon with a knife, or the heaped ones will push you well past the number.

That’s a decent backup for small amounts, a few tablespoons stirred into a bowl of oats, say. For a full cup it’s a lot of scraping. A scale is quicker, and it spares you the sticky measuring cup that never quite comes clean.

Quick wrap up

For a smooth, stirred jar the number is 258 g, and half a cup is 129 g. Natural jars need a stir, and reduced fat jars need a scale. That’s how many grams in a cup of peanut butter plays out, jar by jar. Weigh it, and the fundraiser takes care of itself.