BIZOMAT MAKEOS · Materials
ASTM Grain Size Number
What ASTM grain size number does this count or intercept measurement give?
ASTM E112 grain size number G from grains per square inch at 100×, grains per mm² at 1×, or the mean lineal intercept length, with the equivalent values.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Measurement | choice | Which measurement you made. |
| Measured value | The measured number: grains per in² at 100×, grains per mm², or mean intercept length in micrometres. |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
What this means: Measurement
- What it is
- Which kind of grain count or measurement you made on the polished and etched specimen, so the tool applies the matching relation.
- Units and format
- Choose one of 3 options from the list: Grains per square inch at 100×; Grains per mm² at 1×; Mean lineal intercept length (µm).
- Example
- The form opens with “Grains per square inch at 100×” selected as a worked example. Choose the option that matches your case.
- Get it right
- The value you enter must match the method chosen here: a count at 100× is not the same as grains per mm² at 1×.
What this means: Measured value
- What it is
- The measured result in the form chosen above: grains per square inch on the image at 100×, grains per square millimetre of real surface, or the mean lineal intercept length in micrometres.
- Units and format
- Enter a plain number with no unit. The form accepts 0.000001 or more. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 64 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- More grains per area gives a higher grain size number; a longer intercept gives a lower one.
- Get it right
- Average several fields of view before entering. For the intercept method enter micrometres, not millimetres.
Method and formulas
- From a 100× count: G = 1 + log₂(n).
- From grains per mm² at 1×: G = 3.321928 log₁₀(N_A) − 2.954.
- From mean intercept ℓ (mm): G = −6.643856 log₁₀(ℓ) − 3.288.
- Example: 64 grains per in² at 100× is ASTM G 7.
Limitations
- The planimetric and intercept relations agree only approximately; report the method used.
- Assumes equiaxed grains; elongated or duplex structures need the standard’s special procedures.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Report grain size from a micrograph count
- Convert between grain size measures
- Check a material certificate requirement
Who it is for
- Metallurgists
- Quality inspectors
- Materials engineers
What you get
- ASTM grain size number G
- Grains per mm² and per in² at 100×
- Mean lineal intercept
Interpreting the result
- A larger G means finer grains.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 369–380. Topic reference; no source tables or recommended settings are reproduced.
- ASTM E112 Standard Test Methods for Determining Average Grain Size
Learn the Concepts Behind This Tool
These BIZOMAT Library readings explain the method this tool uses, with worked examples.
Method explained here · BIZOMAT original book
Grain size by counts and intercepts
In Microstructures by the Numbers
What it covers: Measuring grain size by counting grains in a known area or boundaries crossed by test lines, converting both to the ASTM grain size number, and the precision of each.
Method explained here · BIZOMAT original book
Hardness and grain size
In Yield and Plastic Flow by the Numbers
What it covers: What a hardness test measures and how far it predicts strength, how grain size raises yield strength by the Hall–Petch relation, and why a coarse-grained heat passed a hardness check.
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