Ounces to Grams for Cooking and Shipping

Why does a US recipe say “8 oz of flour” while the same recipe in Europe says “227 g”? Both numbers describe the exact same pile of flour on the counter. The only thing that changed is the measuring system, and once you know the exact conversion factor, you can move between the two in seconds. This mix-up shows up constantly in cookbooks, on nutrition labels, and on shipping paperwork, and getting it wrong can throw off a recipe or add unexpected postage costs.

This guide covers the ounce you see on a kitchen scale or a shipping label: a unit of weight. We will also clear up a mix-up that trips up a lot of home cooks, the difference between a weight ounce and a fluid ounce.

The Ounces to Grams Formula

The conversion is simple multiplication. Take the number of ounces and multiply by 28.3495 to get grams.

Grams = Ounces x 28.3495

This factor is not rounded or estimated. It comes from the internationally agreed weight of the avoirdupois pound, which is fixed at exactly 453.59237 grams. Since one pound has 16 ounces, dividing 453.59237 by 16 gives 28.349523125 grams per ounce, which is commonly rounded to 28.3495 for everyday use.

To go the other direction, divide grams by 28.3495 to get ounces. For example, 100 grams divided by 28.3495 equals about 3.5274 ounces.

Avoirdupois Ounce vs Fluid Ounce

Here is the biggest source of confusion. The word “ounce” actually means two different things in the kitchen, and mixing them up can ruin a recipe.

• Avoirdupois ounce (oz): a unit of weight. It measures how heavy something is, on a scale.
• Fluid ounce (fl oz): a unit of volume. It measures how much space a liquid takes up, in a measuring cup.

These two units are only equal for water, and even then only approximately. One fluid ounce of water weighs about 1.043 ounces, close to but not exactly one weight ounce. For a syrup, oil, or flour, the weight of one fluid ounce is often quite different from one weight ounce.

This guide only covers the weight ounce, the one used for food ingredients on a scale and for shipping package weights. If a recipe lists “8 fl oz of milk,” that is a volume measurement, not the 28.3495 gram weight factor covered here.

Why the US Uses Ounces and Other Countries Use Grams

The United States is one of the few countries that still uses ounces and pounds as its everyday weight units, largely from historical habit rather than technical necessity. Most other countries switched to the metric system decades ago, so their recipes and shipping labels use grams and kilograms instead.

Grams are popular worldwide because the metric system scales cleanly by powers of ten. There is no need to remember that 16 ounces make a pound. You just move the decimal point: 1000 grams make one kilogram.

Because global cookbooks, imported ingredient labels, and international shipping carriers often use grams, knowing this one conversion factor helps you follow any recipe or read any package label, no matter where it came from.

A Worked Example: Converting a Recipe

Say a recipe calls for 8 ounces of flour. Multiply 8 by 28.3495 to find the answer in grams.

8 x 28.3495 = 226.796 grams, which is commonly rounded to 227 grams on a kitchen scale.

Now try a shipping example. A small package weighs exactly 1 pound, which is 16 ounces. Multiply 16 by 28.3495.

16 x 28.3495 = 453.592 grams, matching the exact pound definition of 453.59237 grams almost perfectly.

Both examples use the same simple rule: multiply the ounce figure by 28.3495, then round to a sensible number of decimal places for your scale or shipping form.

Quick-Reference Table for Common Ounce Amounts

Keep this table handy for the ounce amounts that show up most often in recipes and package weights.

Why Precision Matters for Shipping Costs

Shipping carriers charge by weight bands, so a small rounding mistake can bump a package into a more expensive tier. A package that weighs 453.6 grams and one that weighs 460 grams might look almost the same, but a carrier’s cutoff could treat them differently.

Many international carriers print both ounces and grams on customs forms, since packages cross borders that use different systems. If you fill out a form by hand, convert carefully rather than rounding early, so the two numbers on the label actually match.

For food shipments, some countries also require a declared weight in grams for customs or tax purposes. Using the exact 28.3495 factor, instead of a rough guess, keeps your paperwork accurate and avoids delays at the border.

Weighing Ingredients Accurately at Home

A digital kitchen scale is the most reliable way to apply this conversion in real life. Most models can switch between ounces and grams with one button, so you rarely need to do the math by hand.

Set the scale to grams, place your bowl on top, and press the tare or zero button so the bowl’s weight does not count. Then add your ingredient until the display shows the gram amount from your converted recipe.

Weighing this way is more accurate than scooping with cups, because a cup of flour can pack down differently each time. Grams measure the true weight, so your baking results stay consistent from batch to batch.

Using the Metric to Imperial Converter Tool

There is no single dedicated ounces-to-grams calculator on this site, but our Metric to Imperial Converter handles weight conversions like this one alongside other everyday units. It will not replace a kitchen scale, but it is a fast way to double-check a conversion before you start cooking or packing a box.

For precise cooking or shipping paperwork, always confirm the exact figure rather than relying on memory alone.

Common Mistakes to Avoid

A few simple mix-ups cause most ounces-to-grams errors. Watch for these when you convert.

• Confusing a weight ounce with a fluid ounce, especially for liquid ingredients.
• Rounding too early in a multi-step recipe, which can stack up small errors.
• Forgetting that a pound is 16 ounces, not 10 or 12.
• Using a food’s fluid ounce volume as if it were its weight in ounces.

When in doubt, weigh the ingredient directly on a scale that shows grams. That removes any guessing from the conversion.

Related Conversions You Might Need

This guide sticks to weight, but you may run into other unit questions while cooking, shipping, or traveling. Our sibling guides cover those in full detail.

• Need to convert length instead of weight? See our Feet to Meters Conversion Guide.
• Working with liquid volume instead of fluid ounces? See Liters to Gallons Explained.

Frequently Asked Questions About Ounces to Grams

Sources

This article is for general education only. Conversion factors are standard, but always double-check exact figures for critical uses like recipes, shipping, or legal documents. Reviewed for accuracy by Prof. Dr. Khalil Mudassar, PhD. Last updated September 13, 2026.