One fluid ounce of peanut butter is 32.25 grams, so converting fluid ounces of peanut butter to grams means multiplying by 32.25. That factor is specific to this ingredient — it comes from its density, not from any relationship between the two units.
The density behind that figure is 1.0905 g per mL, against 1.00 for water. A cup of water weighs 236.6 g and a cup of peanut butter weighs 258 g, so this ingredient is 109.1% as heavy as the same volume of water — the single fact the whole page rests on.
This is the pair that catches people out. A fluid ounce is a volume and an ounce is a weight, and they are only the same number for something with the density of water. One fluid ounce of peanut butter weighs 1.138 oz, so the two readings differ by 13.8% — worth knowing before trusting a recipe that just says "oz".
Grams are the unit this conversion is really for. A domestic scale resolves to a gram, which is 0.388% of a cup of peanut butter, so weighing gets an accuracy no measuring cup can reach. A 500 g pack of it is 1.938 cups, and a 1 kg pack 3.876.
What the number depends on: Smooth, at room temperature. Straight from the fridge it is far harder to level into a cup, and that shows up on the scale.
The formula
fluid ounces- The amount of peanut butter you are converting, in fluid ounces
32.25- Grams per fluid ounce for peanut butter, from its density of 1.0905 g/mL
grams- The equivalent quantity in grams
How it works, step by step
- Enter the quantity in fluid ounces.
- It is multiplied by 32.25, the grams-per-fluid ounce figure for peanut butter.
- The result appears in grams, with a second reading in oz beneath it.
- Use the measure table if you want a standard recipe quantity rather than a number you type in.
Worked examples
3 fl oz of peanut butter in grams
3 fl oz of peanut butter weighs out at 96.75 grams. Divide 96.75 by 32.25 and you get back to 3 fl oz, which is the quickest check that the factor is the right way up.
6 fl oz of peanut butter in grams
6 fl oz of peanut butter weighs out at 193.5 grams. Divide 193.5 by 32.25 and you get back to 6 fl oz, which is the quickest check that the factor is the right way up.
12 fl oz of peanut butter in grams
Take 12 fl oz of peanut butter: 12 × 32.25 gives 387 grams. Doubling the batch takes it to 774 grams, because the relationship is a straight proportion once the density is known.
How to read your score
Frequently asked questions
How many grams are in 1 fl oz of peanut butter?
One fluid ounce of peanut butter is 32.25 grams. Half that quantity is 16.125 grams and double it is 64.5 grams, so the figure scales straight up and down — there is no offset in this conversion, only the factor.
Why is a cup of peanut butter not 236 g like water?
Because weight per cup depends on what is in the cup. Peanut butter has a density of 1.0905 g per mL where water has 1.00, so a cup of it weighs 258 g rather than 236.6 g. That is a difference of 21.4 g per cup, and it is the reason a single volume-to-weight factor cannot be applied to every ingredient.
Does how I measure it change the weight?
Barely. Peanut butter does not compress, so a cup of it is 258 g however it is poured — within about 1%, which is inside the accuracy of a domestic scale. This is the group where measuring by volume is defensible.
Is a fluid ounce of peanut butter the same as an ounce?
No. A fluid ounce is a volume — one eighth of a US cup, 29.57 mL — and an ounce is a weight. One fluid ounce of peanut butter weighs 1.138 oz, so the two readings differ by 13.8%. They coincide only for something with the density of water, and then only roughly.
Is this a US cup or a metric cup?
US customary: 236.59 mL, which is the cup every US recipe means. A metric cup is 250 mL, so the same cup of peanut butter would weigh 272.63 g instead of 258 g — 14.6 g more, or 5.67%. Australian and some European recipes use the metric cup, and the difference is large enough to matter in baking.
Do I need a scale for this, or will measuring cups do?
A scale, if the result matters. Volume measuring carries a spread of about 1% for peanut butter — roughly 2.58 g on a 258 g cup — while a domestic scale is accurate to a gram or two. For anything where the ratio of ingredients drives the outcome, bread and pastry above all, weigh it.
How many fluid ounces of peanut butter is 500 g?
500 g of peanut butter is 15.504 fluid ounces — 0.0310078 fluid ounces to one gram, so 500 × 0.0310078 = 15.504. Going that way is a division by 32.25, or a multiplication by 0.0310078 if you prefer.
Peanut butter in fluid ounces and grams
| Fluid Ounces | Grams | Unrounded |
|---|---|---|
| 1 fl oz | 32.25 g | 32.25 |
| 2 fl oz | 64.5 g | 64.5 |
| 3 fl oz | 96.75 g | 96.75 |
| 4 fl oz | 129 g | 129 |
| 6 fl oz | 193.5 g | 193.5 |
| 8 fl oz | 258 g | 258 |
| 12 fl oz | 387 g | 387 |
| 16 fl oz | 516 g | 516 |
Based on 258 g per cup of peanut butter. One fluid ounce of peanut butter is 32.25 grams.
| Measure | Grams | Ounces | Millilitres |
|---|---|---|---|
| 1 cup | 258 g | 9.1 oz | 236.6 mL |
| 3/4 cup | 193.5 g | 6.83 oz | 177.4 mL |
| 2/3 cup | 172 g | 6.07 oz | 157.7 mL |
| 1/2 cup | 129 g | 4.55 oz | 118.3 mL |
| 1/3 cup | 86 g | 3.03 oz | 78.86 mL |
| 1/4 cup | 64.5 g | 2.28 oz | 59.15 mL |
| 1 tbsp | 16.12 g | 0.569 oz | 14.79 mL |
| 1 tsp | 5.375 g | 0.19 oz | 4.929 mL |
US customary measures: 1 cup = 236.59 mL, 1 tbsp = 14.79 mL, 1 tsp = 4.93 mL.
| Ingredient | Grams per cup | Ounces per cup | Density (g/mL) |
|---|---|---|---|
| Tomato sauce | 245 g | 8.642 oz | 1.036 |
| Orange juice | 248 g | 8.748 oz | 1.048 |
| Evaporated milk | 252 g | 8.889 oz | 1.065 |
| Peanut butter (this page) | 258 g | 9.101 oz | 1.091 |
| Sweetened condensed milk | 306 g | 10.79 oz | 1.293 |
| Maple syrup | 322 g | 11.36 oz | 1.361 |
| Corn syrup | 328 g | 11.57 oz | 1.386 |
Ordered by weight. The spread across this group is why a single generic cups-to-grams factor cannot work.