How Many Grams of Fat Per 100 Calories is Low Fat?

January 10, 2026 •

4 min read

According to a general guideline used by many nutritionists, a food is considered low-fat if it contains 3 grams of fat or less for every 100 calories. This easy-to-remember benchmark is a helpful tool for quickly evaluating the fat density of different foods, complementing the official definitions found on food packaging.

Quick Summary

This article explains the standard 3-gram rule for low-fat foods per 100 calories, detailing how to calculate fat percentages from nutrition labels and contrasting this method with the official FDA 'per serving' definition for informed dietary decisions.

Key Points

The 3 Gram Rule: A food is commonly considered low fat if it contains 3 grams of fat or less per 100 calories.
Calculation: To find the fat percentage, multiply grams of fat by 9, divide by total calories, then multiply by 100.
FDA Definition: The official U.S. 'Low Fat' claim means 3 grams of fat or less per serving, not per 100 calories.
Read Labels Carefully: Small serving sizes can make a high-fat food appear 'low-fat' according to official definitions; always consider the full nutrition facts.
Beware Added Sugar: Many 'low fat' products compensate for flavor by adding sugar, which may result in a similar or higher calorie count.
Whole Foods First: Naturally low-fat whole foods, like fruits and vegetables, often negate the need for complex label analysis.

The 3 Grams Per 100 Calories Rule Explained

The 3 grams of fat per 100 calories rule is a straightforward way to assess the nutritional value of a food, focusing on its fat concentration rather than relying solely on the manufacturer's chosen serving size. A key fact to remember is that each gram of fat contains 9 calories. This means that 3 grams of fat contribute 27 calories. On a per-100-calorie basis, this equates to 27% of the total calories coming from fat, which aligns with general health recommendations that suggest keeping daily fat intake below 30% of total calories. By focusing on this metric, you can make an apples-to-apples comparison between different products, even if their serving sizes vary wildly.

Calculating Your Food's Fat Percentage

To apply this rule, you need to read a nutrition label. Here is a simple, step-by-step process:

Locate the Information: Find the 'Serving Size', 'Calories', and 'Total Fat' sections on the nutrition label.
Find the Grams of Fat: Note the number of grams of fat listed per serving.
Find the Calories: Note the total calories listed per serving.
Do the Math: Multiply the grams of fat by 9 to get the calories from fat. Divide this number by the total calories. Multiply the result by 100 to get the percentage of calories from fat.
- Example: If a serving has 5 grams of fat and 150 calories: (5g fat 9 cal/g) / 150 cal = 45 / 150 = 0.3. Then, 0.3 100 = 30%. This item has 30% of its calories from fat.
Assess: Compare your final percentage to the 30% benchmark to determine if the food is relatively low in fat density.

The FDA's Official 'Low Fat' Definition

It is crucial to differentiate between the useful rule of thumb and the official standard used for labeling. The U.S. Food and Drug Administration (FDA) has a specific regulation for using the 'Low Fat' claim on food packaging. The FDA defines a 'Low Fat' food as one that contains 3 grams of fat or less per labeled serving. For products with very small serving sizes, the food must also meet the 3-gram fat threshold per 50 grams of food to prevent misleading claims.

This official definition can sometimes be less informative for consumers than the per-100-calorie rule. For instance, a product could have a very small serving size, allowing it to legally be labeled 'Low Fat' even if its overall fat content is quite high. If you eat multiple servings, your total fat intake could be substantial. This is a common pitfall that consumers face when only glancing at the front-of-package claims.

Comparing Low-Fat Metrics: Per 100 Calories vs. Per Serving

Understanding the differences between these two metrics is key to making informed decisions. The table below highlights their main features, benefits, and potential drawbacks.


Metric	Per 100 Calories (Rule of Thumb)	FDA's Per Serving Rule
Grams of Fat	3g or less	3g or less
Basis of Measurement	Standardized 100-calorie portion	Stated serving size on package
Benefit	Allows for easy comparison of fat density between different foods, eliminating serving size discrepancies.	Official regulatory standard for food labeling, ensuring consistency in product claims.
Potential Drawback	Not an official claim; needs manual calculation and can be hard to apply to high-calorie or high-fat foods.	Can be misleading if serving size is small, making a high-fat food appear 'low-fat'.

Practical Application: Making Smarter Choices

Beyond simply knowing the numbers, the true value lies in applying this knowledge to your daily routine. Here are some actionable tips for incorporating this understanding into your eating habits:

Read Beyond the Label: Never rely solely on front-of-package claims like 'Low Fat' or 'Light'. Always turn the package over to check the full nutrition facts panel.
Beware of Sugar: Be aware that many 'Low Fat' and 'Fat Free' products replace fat with added sugars to maintain flavor. Always check the sugar content to ensure you aren't trading one nutritional issue for another.
Prioritize Whole Foods: Whole, unprocessed foods like fruits, vegetables, and lean meats are often naturally low in fat. Prioritizing these foods reduces the need to analyze labels for fat content.
Do the Comparison Test: Next time you are in the grocery store, compare two similar products using the per-100-calorie method. For example, compare a standard yogurt with a low-fat one to see the real fat density difference.

Conclusion

In conclusion, understanding how many grams of fat per 100 calories is low fat is a powerful tool for navigating the often-confusing world of food labels. The 3-gram-per-100-calorie rule provides a practical, universal benchmark for assessing a food's fat density, offering a more nuanced perspective than the FDA's 'per serving' definition. While both metrics have their place, combining them with a mindful approach to label reading will empower you to make truly healthier and more informed food choices. This knowledge moves you beyond marketing claims to make decisions based on solid nutritional principles.

For more comprehensive dietary information, you can visit the American Cancer Society on Low-Fat Foods.

Frequently Asked Questions

To calculate the percentage of calories from fat, multiply the grams of fat by 9 (since each gram of fat has 9 calories). Then, divide that number by the food's total calories and multiply by 100.

The FDA defines a food as 'Low Fat' if it contains 3 grams of fat or less per labeled serving. The 'per serving' basis can be misleading if the serving size is small.

This rule provides a consistent way to compare the fat density of different foods, regardless of their package-specific serving sizes. It's a quick tool for assessing nutritional quality.

No, not necessarily. Many products labeled as 'low-fat' or 'fat-free' replace the fat with added sugars to improve taste. This can result in a calorie count similar to or even higher than the regular version.

A 'Low Fat' product contains 3 grams of fat or less per serving, while a 'Fat Free' product must have less than 0.5 grams of fat per serving.

Yes. If a product's serving size is small enough to keep the fat content below 3 grams, it can be legally labeled 'Low Fat.' This can be misleading if you consume multiple servings, accumulating a high total fat intake.

While many naturally low-fat foods are healthy, it's important to consider their overall nutritional profile. Check for high levels of sugar, sodium, or other additives that might compromise the health benefits.