ASTM Grain Size Calculator
64 grains per square inch at 100× is an ASTM grain size of G = 7, a mean intercept of about 28 µm.
7
- Grains per in² at 100×, 2^(G−1)
- 64
- Grains per mm² at 1×
- 992.001984
- Mean lineal intercept ℓ (ASTM E112)
- 28.28144908 µm
- Average grain diameter (≈ ℓ)
- 28.28144908 µm
Step-by-step solution
- N = 2^(G − 1) → G = 1 + log₂ N = 7
- Grains per mm² at 1× = 2^(G − 1) ÷ 0.064516 = 992.001984
ASTM Grain Size Formula
N = 2^(G − 1) grains/in² at 100×
G = −6.6439 log₁₀ ℓ − 3.288 (ℓ in mm); grains per mm² = 2^(G + 2.954)
Worked Example
A micrograph showing 64 grains per square inch at 100×:
- N = 2^(G − 1) → G = 1 + log₂ N = 7
- Grains per mm² at 1× = 2^(G − 1) ÷ 0.064516 = 992.001984
Grains per mm² at 1×: 992.001984 · Mean lineal intercept ℓ (ASTM E112): 28.28144908 µm · Average grain diameter (≈ ℓ): 28.28144908 µm
GATE tip
Combine with Hall–Petch: refining from G = 5 to G = 9 cuts the intercept length about fourfold and roughly doubles the grain-boundary strengthening term.
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Frequently asked questions
Does a higher G mean finer grains?
Yes: each step up doubles the number of grains per area. G 1–3 is coarse, 7–8 fine; most structural steels are 6–9.
What if the micrograph is not at 100×?
Scale the count by (M/100)² to the equivalent at 100×, which the magnification input does.
Sources
- The International System of Units (SI), 9th edition (SI Brochure), Bureau International des Poids et Mesures .
Last reviewed: . Factors are stored exactly and computed with 50-digit decimal arithmetic. See how we verify conversion factors.
Cite this page
APA
Scientific Converters. (2026, October 15). ASTM Grain Size Calculator. Retrieved October 25, 2026, from https://scientificconverters.com/calculators/astm-grain-size-calculator/
IEEE
Scientific Converters, "ASTM Grain Size Calculator," scientificconverters.com. Accessed: Oct. 25, 2026. [Online]. Available: https://scientificconverters.com/calculators/astm-grain-size-calculator/