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Safety First: Ammunition reloading is dangerous. Always cross-reference data with official reloading manuals. Never exceed published load data. This tool is for reference only.
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About

The grain (gr) is a unit of mass that, while ancient, remains the standard in highly specific fields like ballistics, ammunition reloading, and archery. For professionals and hobbyists in these areas, converting between grains and grams (g) is not a matter of simple preference, it is a matter of safety and performance. The weight of bullets, arrowheads, and, most critically, gunpowder charges are measured in grains. An inaccurate conversion can lead to dangerous pressure levels in a firearm or inconsistent arrow flight.

This tool is built for the precision required in these applications. It provides high-accuracy conversions and includes features relevant to the user, such as a quick-swap button to reverse the calculation and a high-value warning to prevent potentially catastrophic data entry errors. It is designed to be a reliable digital companion on the reloading bench or in the workshop.

grains to grams gr to g reloading calculator ballistics archery arrow weight bullet weight powder charge

Formulas

The conversion is defined by an exact factor established by international agreement.

mg = mgr × 0.06479891

To convert from grams to grains, the inverse operation is used:

mgr = mg0.06479891

Reference Data

Grains (gr)Grams (g)Common Application
6 gr0.389 gTypical powder charge for a .380 ACP pistol round
55 gr3.564 gCommon bullet weight for .223 Remington / 5.56mm NATO
100 gr6.480 gStandard arrowhead (broadhead) weight for hunting
150 gr9.720 gCommon bullet weight for .308 Winchester rifle
230 gr14.904 gStandard bullet weight for .45 ACP
700 gr45.359 gBullet weight for very large caliber rifles like .50 BMG
7000 gr453.592 gExactly equal to one Avoirdupois pound

Frequently Asked Questions

The grain is one of the oldest units of mass, historically based on the weight of a single, ideal seed from a cereal plant. It has been standardized today and is legally defined as exactly 1/7000 of an Avoirdupois pound.
A firearm is designed to withstand a specific maximum pressure. The amount of pressure generated is directly related to the powder charge weight. Even a tiny error in measurement, off by a few grains, can create a dangerous overpressure event, potentially destroying the firearm and injuring the user. Utmost precision is required.
Historically, it was used in pharmacy and chemistry (as the Apothecaries" grain), but this usage is now obsolete in most parts of the world. Its primary modern application is in the fields of internal ballistics and archery.
There are approximately 15.432 grains in one gram. This is a useful number to remember for quick mental estimations.