Convert Grain to Carat (metric)
Convert grains to carats (metric) instantly. 1 grain = 0.3239945 carat (metric) — use the live calculator, the exact formula, a conversion table and worked examples. Also check the Carat (metric) to Grain converter for the reverse conversion.
Units explained
Grain
The grain (gr) equals 1/7000 of an avoirdupois pound, about 64.8 milligrams.
Based on the nominal mass of a single barley grain.
Ammunition and bullet mass, archery, and historical pharmacy.
Standardized through the English avoirdupois system and retained in 1959.
Carat (metric)
The metric carat (ct) equals exactly 200 milligrams (0.0002 kg).
From Arabic 'qirat' and Greek 'keration', the carob seed once used as a counterweight.
The worldwide standard for gemstone and diamond mass.
The metric carat was fixed at 200 mg internationally in 1907.
Grain to Carat (metric) conversion formula
The relationship between grains and carats (metric):
To convert grains to carats (metric), multiply the value in grains by 0.3239945. To reverse, multiply carats (metric) by 3.0864721469.
How to use this converter
Type a value into the calculator. The result in carats (metric) updates as you type. Tap a quick value, copy the result with one click, or use the swap arrow to jump straight to the Carat (metric) to Grain converter for the reverse direction.
Step-by-step: convert grains to carats (metric)
- Write down the value in grains (gr).
- Multiply that value by the factor 0.3239945.
- The product is the equivalent value in carats (metric) (ct).
- To reverse, multiply the carat (metric) value by 3.0864721469.
Worked examples
Example 1 — Convert 1 gr to ct:
1 × 0.3239945 = 0.3239945 ct
Example 2 — Convert 100 gr to ct:
100 × 0.3239945 = 32.39945 ct
Real-world example — Hair-width scale measurements
A 70-grain measurement (about the diameter of a human hair) is the kind of value materials engineers regularly express in adjacent micro-scale units like carats (metric) for direct comparison across supplier datasheets.
70 gr × 0.3239945 = 22.679615 ct
Real-world example — Paper and film thicknesses
At the thickness of office paper (roughly 3 grains), converting between sub-millimeter units is routine for packaging and printing buyers comparing quotes from metric and US suppliers.
3 gr × 0.3239945 = 0.9719835 ct
Real-world example — Plastic-film thickness alternates
A 150-grain plastic film converts cleanly to carats (metric) — useful for packaging buyers reconciling supplier datasheets across metric and US measurement systems.
150 gr × 0.3239945 = 48.599175 ct
Grain to Carat (metric) conversion table
Standard reference values for converting grains to carats (metric):
| Grain [gr] | Carat (metric) [ct] |
|---|---|
| 0.01 | 0.003239945 |
| 0.1 | 0.03239945 |
| 1 | 0.3239945 |
| 2 | 0.647989 |
| 3 | 0.9719835 |
| 4 | 1.295978 |
| 5 | 1.6199725 |
| 10 | 3.239945 |
| 20 | 6.47989 |
| 30 | 9.719835 |
| 40 | 12.95978 |
| 50 | 16.199725 |
| 100 | 32.39945 |
| 500 | 161.99725 |
| 1000 | 323.9945 |
Frequently asked questions
How many carats (metric) is 1 grain?
How do I convert grains to carats (metric)?
How do I convert carats (metric) back to grains?
How many carats (metric) is 100 grains?
Popular weight unit conversions
Convert Grain to other weight units
Show all Grain conversions
Metric / SI (18 units)
Avoirdupois (14 units)
Troy & Apothecary (10 units)
Indian / South Asian (6 units)
Scientific / Atomic (9 units)
Astronomical (4 units)
Biblical / Ancient (14 units)
Sources & references
Conversion factor (1 gr = 0.3239945 ct) verified against the following authoritative sources:
- BIPM — The International System of Units (SI Brochure 9th ed.)
Official BIPM publication defining the seven SI base units (including the meter) and the rules for their use. The global authority on units of measurement.
- NIST — Guide to the SI
US National Institute of Standards and Technology reference covering the SI base and derived units with definitions and usage rules for US technical practice.
- NIST Special Publication 811 — Guide for the Use of the International System of Units
Detailed NIST guide covering exact conversion factors between SI and US customary units along with formatting and rounding conventions.
- NIST — Refinement of values for the yard and pound (Federal Register 1959)
The treaty (signed by US
- International Astronomical Union — System of Astronomical Constants
The IAU defines astronomical units including the AU (149597870700 m exactly) light-year and parsec used in astronomy and astrophysics.