Mass and Weight · Unit Converter

Convert Atomic Mass Unit to Grain

Convert atomic mass unit to grains instantly. 1 atomic mass unit = 2.562606e-23 grain — use the live calculator, the exact formula, a conversion table and worked examples. Also check the Grain to Atomic Mass Unit converter for the reverse conversion.

Written by Sunith Babu L, Ph.D., Lead Engineer Reviewed by Dr. Ashok Kumar K, Ph.D.

Mass and Weight category 2 min read Published June 10, 2026 Last reviewed June 10, 2026 Updated June 10, 2026

Units explained

Scientific / Atomic

Atomic Mass Unit

What is a atomic mass unit?

One unified atomic mass unit (u) is defined as 1/12 the mass of a carbon-12 atom, about 1.6605E-27 kg.

Origin of the atomic mass unit

Introduced to give atomic and molecular masses convenient numerical values.

Where it is used

Atomic, molecular, and nuclear physics and chemistry.

When and where it was developed

The unified (carbon-12) scale was adopted by IUPAC and IUPAP in 1960-1961.

Avoirdupois

Grain

What is a grain?

The grain (gr) equals 1/7000 of an avoirdupois pound, about 64.8 milligrams.

Origin of the grain

Based on the nominal mass of a single barley grain.

Where it is used

Ammunition and bullet mass, archery, and historical pharmacy.

When and where it was developed

Standardized through the English avoirdupois system and retained in 1959.

Atomic Mass Unit to Grain conversion formula

The relationship between atomic mass unit and grains:

1 u = 2.562606e-23 gr

1 gr = 3.902278e+22 u

To convert atomic mass unit to grains, multiply the value in atomic mass unit by 2.562606e-23. To reverse, multiply grains by 3.902278e+22.

How to use this converter

Type a value into the calculator. The result in grains updates as you type. Tap a quick value, copy the result with one click, or use the swap arrow to jump straight to the Grain to Atomic Mass Unit converter for the reverse direction.

Step-by-step: convert atomic mass unit to grains

Write down the value in atomic mass unit (u).
Multiply that value by the factor 2.562606e-23.
The product is the equivalent value in grains (gr).
To reverse, multiply the grain value by 3.902278e+22.

Worked examples

Example 1 — Convert 1 u to gr:
1 × 2.562606e-23 = 2.562606e-23 gr

Example 2 — Convert 100 u to gr:
100 × 2.562606e-23 = 2.562606e-21 gr

Real-world example — Spanning sub-micron to micron scale

Crossing from atomic mass unit to grains is the everyday workflow of microscopy and semiconductor engineering — a measurement of 1000 atomic mass unit translates to a much more compact value in grains that fits the scale of biological cells and process nodes.

1000 u × 2.562606e-23 = 2.562606e-20 gr

Real-world example — Sub-visible-light wavelength

500 atomic mass unit (the green-yellow visible band) equals 0.5 grains — the canonical conversion in optics between wavelength specifications and micron-scale lens-coating thicknesses.

500 u × 2.562606e-23 = 1.281303e-20 gr

Atomic Mass Unit to Grain conversion table

Standard reference values for converting atomic mass unit to grains:

Atomic Mass Unit [u]	Grain [gr]
0.01	2.562606e-25
0.1	2.562606e-24
1	2.562606e-23
2	5.125211e-23
3	7.687817e-23
4	1.025042e-22
5	1.281303e-22
10	2.562606e-22
20	5.125211e-22
30	7.687817e-22
40	1.025042e-21
50	1.281303e-21
100	2.562606e-21
500	1.281303e-20
1000	2.562606e-20

Frequently asked questions

How many grains is 1 atomic mass unit?

1 atomic mass unit equals 2.562606e-23 grain.

How do I convert atomic mass unit to grains?

Multiply the value in atomic mass unit by 2.562606e-23 to get grains.

How do I convert grains back to atomic mass unit?

Multiply the value in grains by 3.902278e+22, or use the Grain to Atomic Mass Unit converter.

How many grains is 100 atomic mass unit?

100 atomic mass unit equals 2.562606e-21 grains, because 100 × 2.562606e-23 = 2.562606e-21.

Convert Atomic Mass Unit to other weight units

Show all Atomic Mass Unit conversions

Metric / SI (18 units)

Avoirdupois (15 units)

Troy & Apothecary (10 units)

Atomic Mass Unit to Point (1/100 carat) (pt) Atomic Mass Unit to Carat (metric) (ct) Atomic Mass Unit to Scruple (apothecary) (s ap) Atomic Mass Unit to Pennyweight (dwt) Atomic Mass Unit to Momme (mom) Atomic Mass Unit to Mace (mace) Atomic Mass Unit to Dram (apothecary/troy) (dr ap) Atomic Mass Unit to Troy Ounce (oz t) Atomic Mass Unit to Tael (tael) Atomic Mass Unit to Pound (troy/apothecary) (lb t)

Indian / South Asian (6 units)

Atomic Mass Unit to Ratti (ratti) Atomic Mass Unit to Masha (masha) Atomic Mass Unit to Tola (tola) Atomic Mass Unit to Chittack (Chatank) (chittack) Atomic Mass Unit to Seer (Ser) (seer) Atomic Mass Unit to Maund (Mann) (maund)

Scientific / Atomic (8 units)

Atomic Mass Unit to Electron Mass (rest) (me) Atomic Mass Unit to MeV/c2 (MeV/c²) Atomic Mass Unit to Muon Mass (mµ) Atomic Mass Unit to Proton Mass (mp) Atomic Mass Unit to Neutron Mass (mn) Atomic Mass Unit to Deuteron Mass (md) Atomic Mass Unit to Carbon-12 Atom Mass (C-12) Atomic Mass Unit to Planck Mass (mP)

Astronomical (4 units)

Atomic Mass Unit to Lunar Mass (Moon) (M☾) Atomic Mass Unit to Earth's Mass (M⊕) Atomic Mass Unit to Jupiter Mass (MJ) Atomic Mass Unit to Sun's Mass (M☉)

Biblical / Ancient (14 units)

Force / Engineering (5 units)

Atomic Mass Unit to Poundal (pdl) Atomic Mass Unit to Ton (assay) (US) (AT) Atomic Mass Unit to Ton (assay) (UK) (AT) Atomic Mass Unit to Kilogram-force square second/meter (hyl) Atomic Mass Unit to Slug (slug)

Sources & references

Conversion factor (1 u = 2.562606e-23 gr) 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 Hydrographic Organization — Resolution on the Nautical Mile
International authority that standardised the nautical mile at exactly 1852 m in 1929 — the value adopted worldwide for sea and air navigation.

Results are provided for general reference. Verify critical measurements against an authoritative standard.