How many grains are in one ounce?

There are exactly 437.5 grains in one avoirdupois ounce. This is an exact ratio, not an approximation, because both units are defined within the same measurement system.

Why do bullets use grains instead of grams?

The firearms industry adopted grains because the unit provides whole-number precision at the scale relevant to projectile weight without requiring decimals. A 9mm bullet at 124 grains is easier to communicate on a box label than 8.035 grams, and the tradition dates to when gunpowder itself was measured in grains.

Is a grain of weight the same as a grain of wheat?

Historically, yes. The grain was originally defined as the weight of a single grain of barley taken from the middle of the ear. While modern definitions are based on the international avoirdupois pound (1 grain = 64.79891 milligrams exactly), the etymological connection to cereal grains is direct and literal.

Ounces to Grains (oz to gr) Converter

1 oz = 437.5 gr

1 Ounce equals 437.5 Grains (1 oz = 437.5 gr). Convert Ounces to Grains with formula, table, and examples.

One avoirdupois ounce equals exactly 437.5 grains. The grain is the smallest traditional unit in both the avoirdupois and troy weight systems, and it is the only unit shared identically between them. This makes it a fundamental bridge unit in historical metrology.

How to Convert Ounces to Grains

gr = oz × 437.5

Multiply the value in Ounces by 437.5

Take your value in Ounces
Multiply by 437.5
Read the result in Grains

Common Ounces to Grains Conversions

Ounces (oz)	Grains (gr)	Status
1 oz	437.5 gr
2 oz	875 gr
5 oz	2,187.5 gr
10 oz	4,375 gr
25 oz	10,937.5 gr
50 oz	21,875 gr
100 oz	43,750 gr
500 oz	218,750 gr
1,000 oz	437,500 gr

Good to Know About Ounces to Grains Conversion

The grain is one of the oldest weight units still in active commercial use. Its origin in barley grains connects modern ammunition boxes and pharmaceutical labels to Bronze Age merchants who balanced seeds on primitive scales. The 1959 international yard and pound agreement fixed the grain at exactly 64.79891 milligrams, finally giving this ancient unit a precise modern definition.

Ounces to Grains: What You Need to Know

Ammunition manufacturers specify bullet weights in grains, with common rifle rounds ranging from 55 grains for a .223 Remington to 220 grains for a .30-06 heavy load. Archers select arrow points by grain weight to tune flight characteristics. Pharmacists in the United States historically prescribed aspirin doses in grains, where a standard 5-grain aspirin tablet equals approximately 325 milligrams.

What is a Ounce? oz

An imperial and US customary unit of mass equal to approximately 28.35 grams. Commonly used in the US and UK for food and postal weight.

Imperial Us-customary food packaging (US/UK) postal weight cooking (US)

Learn more about Ounce →

What is a Grain? gr

A grain is a unit of mass equal to exactly 64.79891 milligrams. It is the same in the avoirdupois, troy, and apothecaries' systems, derived from the 1959 international agreement defining the pound as exactly 0.45359237 kilograms.

Imperial Troy Apothecaries ammunition weight bullet measurement historical pharmacy

Learn more about Grain →

Going the other way? Use our Grains to Ounces converter.

Ounces to Grains FAQ

There are exactly 437.5 grains in one avoirdupois ounce. This is an exact ratio, not an approximation, because both units are defined within the same measurement system.
The firearms industry adopted grains because the unit provides whole-number precision at the scale relevant to projectile weight without requiring decimals. A 9mm bullet at 124 grains is easier to communicate on a box label than 8.035 grams, and the tradition dates to when gunpowder itself was measured in grains.
Historically, yes. The grain was originally defined as the weight of a single grain of barley taken from the middle of the ear. While modern definitions are based on the international avoirdupois pound (1 grain = 64.79891 milligrams exactly), the etymological connection to cereal grains is direct and literal.

Non-Frequently Asked Questions About Ounces to Grains

Questions nobody should ask - but someone did.

A typical bowl of cereal weighing about 2 ounces contains 875 grains of weight, regardless of how many individual cereal grains sit in the bowl. The word 'grain' doing double duty as both a food category and a weight unit has confused breakfast tables for centuries.
A medieval archer selecting a 350-grain arrow would be holding exactly 0.8 ounces of projectile. Whether they knew that depends on their education, but they certainly understood that heavier arrows hit harder and lighter arrows flew farther, which is the practical knowledge that mattered.
The number 437.5 results from the avoirdupois pound being defined as 7,000 grains divided into 16 ounces. 7,000 divided by 16 is 437.5, which is perfectly clean in fraction form (437 and a half) but admittedly looks untidy in decimal. The imperial system has never prioritized aesthetic appeal.