Grain Size Calculator
Calculate ASTM grain size numbers and convert between different grain size measurements using ASTM E112 standard methods. Grain size significantly affects material properties including strength, toughness, and ductility.
Range: 0 to 14 (ASTM E112). Results are actual (specimen-scale) sizes.
About Grain Size Measurement
Grain size is a critical microstructural parameter that affects material properties. ASTM E112 provides standardized methods for determining average grain size:
- ASTM Grain Size Number (G): Logarithmic scale where G = log₂(N) + 1, where N is grains per square inch at 100x (equivalently, NA = 15.50 × 2G−1 grains per mm² at 1x)
- Intercept (Heyn) Method: Count grain-boundary intersections along test lines; triple-point intersections count as 1.5. G = −6.6439·log₁₀(ℓ) − 3.288, with ℓ the mean lineal intercept in mm at 1x
- Planimetric (Jeffries) Method: Count grains within a known test area — grains inside count 1, grains cut by the boundary count ½. G = 3.3219·log₁₀(NA) − 2.954
- Comparison Method: Compare microstructure to standard charts
Sample preparation: Reliable grain size measurement requires a deformation-free, uniformly etched surface with clearly delineated grain boundaries. Residual polishing deformation or uneven etching will bias both intercept and planimetric counts.
Note: This calculator uses formulas from ASTM E112. For official grain size determination, follow the complete ASTM E112 standard procedures.
Need More Help?
Learn more about microstructural analysis and grain size measurement in our guides.
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