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ASTM E112 Grain Size Analyzer.

Upload a metallographic micrograph and measure grain size using the Heyn intercept method. Client-side processing — images never leave your browser.

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Place your micrograph

Drag & drop or click to browse — JPEG, PNG

When to use

Measure ASTM grain size number from metallographic micrographs
Apply the Heyn intercept method with digital test lines
Analyze grain size distribution across multiple fields of view
Generate reports conforming to ASTM E112 standard requirements
Process both optical and SEM metallographic images

Do not use for

Non-metallic grain structures (ceramics, polymers)
Heavily deformed or amorphous microstructures
Phase analysis or phase fraction measurement (use image thresholding)

Always calibrate the scale bar before measuring

The most common source of error is incorrect pixels-per-micron calibration. If your micrograph has a scale bar, measure it in pixels and enter the known length. An incorrect calibration will systematically shift all grain size numbers — the intercept lengths scale linearly with the calibration factor.

Count at least 50 intercepts per specimen

ASTM E112 requires a minimum of 50 grain boundary intersections for a statistically reliable measurement. With fewer intercepts, the standard deviation of the grain size estimate becomes unacceptably large. Use multiple test lines across at least 3 fields of view to reach this threshold.

Grain boundary contrast must be adequate

Faint or incomplete grain boundaries lead to missed intersections and overestimated grain size (lower G number). If boundaries are hard to see, the specimen likely needs re-etching. Nital for carbon steels, Kalling’s No. 2 for stainless steels, and Keller’s reagent for aluminum alloys are standard choices.

Select representative fields of view

Avoid measuring only in regions that look “typical” by eye. ASTM E112 specifies random or systematic field selection to avoid sampling bias. If the microstructure is heterogeneous (e.g., banded or duplex grain size), report the range and consider ASTM E1181 for characterizing grain size distributions.

ASTM Grain Size Number Reference

G Number	Avg. Diameter (mm)	Grains / mm²
-3	1	1
-2	0.75	2
-1	0.5	4
0	0.36	8
1	0.25	16
2	0.18	32
3	0.125	64
4	0.091	128
5	0.062	256
6	0.044	512
7	0.031	1,024
8	0.022	2,048
9	0.016	4,096
10	0.011	8,192
11	0.008	16,384
12	0.006	32,768
13	0.004	65,536
14	0.003	131,072

Method

Heyn linear intercept method per ASTM E112-13. User draws test lines on the uploaded micrograph; grain boundary intersections are counted to compute mean intercept length, which maps to the ASTM grain size number via the standard conversion formula: G = −6.6457 × $\log_{10}$ (ℓ) − 3.298. All image processing uses the browser Canvas API — no server upload.

Published

Published 2026-03-20. Calculations support planning and documentation; verify procurement decisions against manufacturer specifications or institutional SOPs.

How to cite

How to Cite

ConductScience ASTM E112 Grain Size Analyzer. ConductScience, Inc. 2026. Available at: https://conductscience.com/tools/astm-e112-grain-size-analyzer

ASTM E112-13. Standard Test Methods for Determining Average Grain Size. ASTM International, West Conshohocken, PA. doi:10.1520/E0112-13R21

What is ASTM E112 Grain Size Analysis?

ASTM E112 (“Standard Test Methods for Determining Average Grain Size”) is the definitive standard for measuring grain size in metals and alloys. Grain size directly affects mechanical properties — yield strength, hardness, ductility, and fatigue resistance all depend on it. The Hall–Petch relationship predicts that finer grains produce stronger metals.

Materials scientists, quality control engineers, and metallurgists use grain size measurements for incoming inspection, process control, failure analysis, and compliance with specifications in aerospace (AMS), automotive (IATF 16949), and nuclear (ASME) industries.

How the Intercept Method Works

The Heyn intercept method is the most objective of the three ASTM E112 approaches. A set of straight test lines of known total length is placed on the micrograph. Each grain boundary crossing is counted. The mean intercept length is:

ℓ = L / N

where L is the total test line length (corrected for magnification) and N is the total number of boundary intersections. The ASTM grain size number G is then calculated from:

G = −6.6457 ×

\log_{10}

(ℓ) − 3.298

where ℓ is in millimeters. A higher G number means finer grains. Most engineering alloys fall between G = 1 (coarse) and G = 14 (ultrafine).

Frequently asked

What is ASTM E112?

ASTM E112 is the standard test method for determining average grain size in metallic materials. It defines three methods: comparison, planimetric (Jeffries), and intercept (Heyn). This tool implements the intercept method, which is the most objective and reproducible of the three.

How does the intercept (Heyn) method work?

Test lines of known length are drawn across the micrograph. The number of times each line crosses a grain boundary is counted. The mean intercept length (total line length ÷ total intersections) is then converted to an ASTM grain size number using the formula: G = −6.6457 ×

\log_{10}

(ℓ) − 3.298, where ℓ is the mean intercept length in mm.

How do I calibrate the scale?

You need to know the pixels-per-micron ratio for your micrograph. If your image has a scale bar, measure its length in pixels (using any image viewer) and divide by the labeled length in microns. For example, a 100µm scale bar that spans 200 pixels gives 2.0 px/µm.

Are my images uploaded to a server?

No. All processing happens entirely in your browser using the Canvas API. Your micrograph images never leave your computer. This tool works offline after the page loads.

What image formats are supported?

JPEG and PNG. For best results, use uncompressed PNG images. JPEG compression artifacts can interfere with grain boundary detection at high sensitivity settings.

How accurate is this tool?

This is a simplified implementation of the ASTM E112 intercept method intended for quick estimates and educational use. For formal compliance reporting, use a validated commercial tool with calibrated optics. Results depend heavily on image quality, etching quality, and correct scale calibration.

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