In weight measurement, 1 avoirdupois ounce equals exactly 28.349523125 grams.
If you’re weighing ingredients, mailing a parcel, or double-checking a nutrition label, knowing the exact grams per ounce saves time and avoids rounding errors. Below you’ll find the precise figure, a handy conversion table, clear formulas, and the key differences between the everyday ounce used for mass, the troy ounce used for precious metals, and the fluid ounce used for volume.
Grams Per Ounce: The Exact Number
The everyday ounce in the U.S. and many recipes is the avoirdupois ounce. It is defined as exactly 28.349523125 grams. That value isn’t an estimate; it’s a fixed definition published by national standards bodies. If you prefer to work in the other direction, one gram equals 0.03527396195 ounces (avdp). Both conversions give you consistent results across scales, recipes, and calculators. Authoritative tables from the National Institute of Standards and Technology confirm the exact figure for the avoirdupois ounce, so you can rely on it for precise work (NIST mass table).
Where The Number Comes From
The ounce is tied to the pound. One avoirdupois pound is defined as exactly 0.45359237 kilograms, and one pound contains 16 ounces. Divide 0.45359237 kg by 16 and convert kilograms to grams to land on 28.349523125 g per ounce. Because these are definitions, not measurements, the digits don’t change.
Quick Ways To Convert In Your Head
- Ounces → grams: multiply by 28.35 for a close daily-use result. For lab-grade precision, use 28.349523125.
- Grams → ounces: divide by 28.35 or multiply by 0.035274.
Fast Reference Table (Mass, Not Volume)
This chart converts common ounce amounts to grams using the exact definition. It’s perfect for kitchen scales, postage, or hobby projects.
| Ounces (avdp) | Grams |
|---|---|
| 0.25 oz | 7.087381 g |
| 0.5 oz | 14.174762 g |
| 0.75 oz | 21.262143 g |
| 1 oz | 28.349523 g |
| 1.5 oz | 42.524285 g |
| 2 oz | 56.699046 g |
| 3 oz | 85.048569 g |
| 4 oz | 113.398092 g |
| 5 oz | 141.747615 g |
| 6 oz | 170.097139 g |
| 8 oz (½ lb) | 226.796185 g |
| 10 oz | 283.495231 g |
| 12 oz | 340.194277 g |
| 14 oz | 396.893323 g |
| 16 oz (1 lb) | 453.592370 g |
Why People Mix Up Ounces, Grams, And Fluid Ounces
Two different ideas share the word “ounce.” One is mass (what a solid weighs). The other is fluid ounce, which is volume (space a liquid occupies). A bottle marked “6 fl oz” is telling you how many milliliters of liquid are inside, not its weight in grams. U.S. labeling rules use “oz” for weight and “fl oz” for volume to keep them distinct; the regulations even give examples like “Net wt. 6 oz” and “6 fl oz” so shoppers aren’t confused (eCFR 21 CFR 101.7).
Fluid Ounce: A Quick Note
In U.S. packaging and recipes, one fluid ounce equals 29.573529562 milliliters. That’s a volume measure, not a mass measure. If you’re converting a liquid to grams, you need density. Water at room temperature is close to 1 g per mL, so 8 fl oz of water is roughly 237 g. Honey or oil won’t match that because their densities differ. Use “fl oz → mL” first, then multiply by density to get grams.
When The Ounce Isn’t The Same: Avoirdupois Vs. Troy
Most everyday goods use the avoirdupois system. Precious metals often use the troy ounce, which is heavier. A troy ounce is exactly 31.1034768 grams. That figure follows from the grain, a small mass unit set at 64.79891 milligrams by definition. One troy ounce equals 480 grains, so 480 × 0.06479891 g = 31.1034768 g. Standards bodies, trade references, and bullion markets all use this exact relationship. If you weigh coins, bars, or bullion jewelry, make sure your scale and your math use troy units for a true reading.
Which One Should You Use?
- Food, packages, craft supplies: ounces (avdp) ↔ grams.
- Gold, silver, platinum: troy ounces ↔ grams.
- Liquids in bottles: fluid ounces ↔ milliliters, then apply density if you need grams.
Formula Playbook For Accurate Conversions
Mass Conversions (Avoirdupois)
Ounces → grams: g = oz × 28.349523125
Grams → ounces: oz = g ÷ 28.349523125
Mass Conversions (Troy)
Troy ounces → grams: g = ozt × 31.1034768
Grams → troy ounces: ozt = g ÷ 31.1034768
Volume Conversion (Fluid Ounces)
U.S. fluid ounces → milliliters: mL = fl oz × 29.573529562
Milliliters → U.S. fluid ounces: fl oz = mL ÷ 29.573529562
Worked Examples You Can Trust
1) Recipe Calls For 3 Ounces Of Chocolate
You’re using mass. Multiply 3 by 28.349523125 to get 85.048569 g. If your scale shows 85.05 g, you’re on target.
2) Package Lists 200 Grams, But Your Scale Shows Ounces
Divide 200 by 28.349523125. The result is 7.05479 oz. That’s about 7.06 ounces on a digital display.
3) You Bought 2 Troy Ounces Of Silver
Multiply 2 by 31.1034768 to get 62.2069536 g. A standard kitchen ounce figure (28.35 g) would be too low, so always check the unit.
4) A Bottle Says 12 Fl Oz And You Want Grams
First convert to mL: 12 × 29.573529562 = 354.882354744 mL. If the liquid’s density is 1.03 g/mL (some syrups sit near that), the mass is 354.88 × 1.03 ≈ 365.53 g. Same volume, different mass because density differs from water.
Common Pitfalls And How To Avoid Them
Mistake 1: Treating Fl Oz And Oz As The Same Thing
Labels separate them on purpose. “6 oz” is mass. “6 fl oz” is volume. U.S. labeling rules give that exact wording to prevent mix-ups; the examples sit right in the federal regulations so brands keep the distinction clear (eCFR 21 CFR 101.7).
Mistake 2: Using The Kitchen Ounce For Precious Metals
Coins and bars use the heavier troy ounce. If you multiply by 28.35, your gram figure will be short. Use 31.1034768 g per troy ounce instead. Bullion buyers, refiners, and assay labs keep prices and weights in those units for consistency across markets.
Mistake 3: Rounding Too Aggressively
Rounded “28.35 g” works for cooking or postage. If your task needs tighter tolerances, stick with the exact definitions or let a calculator carry full precision and round only at the end.
Differences At A Glance (Use The Right Ounce)
This table puts the three “ounces” side by side so you can select the correct path for your math.
| Unit | What It Measures | Exact Metric Equivalent |
|---|---|---|
| Ounce (avdp) | Mass for everyday goods | 1 oz = 28.349523125 g |
| Troy Ounce | Mass for precious metals | 1 ozt = 31.1034768 g |
| Fluid Ounce (U.S.) | Volume for liquids | 1 fl oz = 29.573529562 mL |
Choosing Tools: Scales, Cups, And Converters
Digital Scales
Pick a scale that displays in grams and ounces, and confirm it can switch to troy ounces if you handle bullion or jewelry. Check the smallest increment: 0.1 g is fine for cooking; 0.01 g is handy for coffee dosing or small-batch baking.
Measuring Cups And Spoons
These measure volume, not mass. They’re great for water-like liquids. For dense syrups, nut butters, or oils, weighing in grams removes guesswork and improves repeatability.
Online Converters
They’re convenient for quick checks, but always confirm which ounce they use. Reputable references publish the same constants you see here. If you want a primary source for the mass ounce definition, the national standards table is the place to look (NIST mass table).
Precision Tips That Prevent Errors
- Zero the scale with your container before you add ingredients.
- Weigh sticky items on a small piece of parchment and subtract that weight.
- Keep units consistent: if you start in grams, stay in grams until the end.
- Write the constant you need on a sticky note: 28.349523125 for mass ounces; 31.1034768 for troy; 29.573529562 for fluid ounces to milliliters.
- Round once, at the end, to match the precision your task needs.
FAQ-Style Clarity Without The FAQ Section
Is 28.35 Good Enough?
Yes for kitchen and postage. For lab work or trade documents, keep full precision or use software that tracks all digits internally.
Why Do Some Recipes Say 30 Grams Per Ounce?
That’s a loose rule of thumb to make math easy. It drifts by about 6% from the real value. If taste or texture matters, use the exact constant. Your bakes will be more consistent across ovens and climates.
What About British Recipes?
Modern British packaging favors grams and milliliters. If a legacy book lists ounces for solids, it’s the same avoirdupois ounce used in U.S. kitchens unless the book specifically calls out troy units for metals or apothecary use.
Takeaway You Can Apply Right Now
For everyday weighing, multiply ounces by 28.349523125 to get grams, or divide grams by that same number to get ounces. If you’re dealing with bullion, switch to 31.1034768. If you see “fl oz,” you’re in volume territory, so convert to milliliters first and bring density into the picture. That’s the clean path to accurate numbers on a scale, in a recipe, or on a label.