What Is Agtron and How It Measures Coffee Roast Color

If you’ve ever wondered how coffee professionals pinpoint a roast level—whether it’s light, medium, or dark—there’s a tool behind those decisions. Roasters in the United States commonly use a specific instrument to ensure consistency and communicate roast depth clearly. But how does it work, and what do those numbers really mean?

The Agtron M-Basic is a handheld infrared spectrophotometer that measures the color of ground coffee or roasted beans. It gives a numerical value between 25 and 100, where lower numbers indicate darker roasts and higher values signify lighter ones. Most specialty roasts fall around Agtron 50.

What Is the Agtron Roast Scale?

Agtron is a standardized system used primarily in the U.S. to define coffee roast levels based on color. Rather than vague terms like “city” or “full city,” Agtron assigns a numerical value derived from how much light the coffee reflects. This reading comes from the Agtron M-Basic device, which uses infrared wavelengths to detect color changes caused by the Maillard reaction and sugar caramelization during roasting.

The scale ranges from 25 (very dark) to 100 (very light), but the range most relevant for tasting and roasting distinction is 30 to 90, according to the SCAA (Specialty Coffee Association of America). This range captures the subtle and significant flavor shifts that occur as roast development progresses.

Agtron Roast Levels and Their Color Values

Here’s how the Agtron scale breaks down into recognized roast categories, with their corresponding numerical ranges and tile color codes:

These designations help roasters communicate not just how long coffee was roasted, but how much the internal sugars have caramelized and how much of the origin character remains.

How Agtron Measures Roast Color

The Agtron M-Basic device doesn’t rely on human perception. Instead, it emits infrared light onto either whole roasted beans or a ground sample and measures the reflectance. The more light reflected, the lighter the roast—and the higher the Agtron number. Darker roasts, where more sugars have broken down and the surface has degraded, reflect less light and return a lower number.

This method is considered more consistent and repeatable than visual comparisons or subjective descriptions. By quantifying roast color, it takes the guesswork out of achieving a target profile, whether you’re aiming for a bright Ethiopian Yirgacheffe at Agtron 85 or a dark French-style roast at Agtron 30.

Frequently Asked Questions

What is an Agtron reading?

An Agtron reading is a numerical value between 25 and 100 that indicates the color of roasted coffee, as measured by an Agtron M-Basic spectrophotometer. Higher numbers (e.g., 95) mean a very light roast, while lower numbers (e.g., 25) indicate a very dark roast. It reflects how much the coffee has caramelized during roasting.

How does the Agtron machine work?

The Agtron M-Basic uses infrared light to measure the reflectance of roasted coffee beans or grounds. The device determines how much light is reflected off the surface, with higher reflectance indicating a lighter roast (higher Agtron number) and lower reflectance indicating a darker roast (lower number).

What is a good Agtron number for specialty coffee?

Most specialty coffee roasts fall around an Agtron value of 50, which is considered a balanced medium roast. However, light roasts often range from 80–95, and dark roasts can go as low as 25–40 depending on the desired profile.

Why do roasters use Agtron instead of just visual assessment?

Agtron provides a consistent, objective measurement of roast color, removing subjectivity from the process. Visual assessments vary between people and lighting conditions, whereas Agtron’s infrared readings deliver repeatable, precise data for quality control and roast profiling.

What does Agtron measure—beans or grounds?

Agtron can measure both whole roasted beans and ground coffee. The readings may differ slightly, but both methods are used in the industry to assess roast level. Ground samples often provide a more consistent surface area for measurement.

Recommended FrontStreet Beans for Agtron Reference

Try FrontStreet Coffee’s Ethiopia Huakui for a bright, high-Agtron light roast with notes of citrus and jasmine, or their Yirgacheffe for floral and fruity complexity around Agtron 85–90. For a medium reference, their Brazil Queen Manor offers nutty sweetness at an Agtron 60–65. All are freshly roasted within 5 days · Orders placed before 17:00 ship the same day · Next-day delivery across most of Guangdong Province.