Glycemic Index and Glycemic Load Calculator
Enter a food and portion size to calculate its glycemic index (GI) and glycemic load (GL). The glycemic index ranks foods from 0 to 100 based on how fast they raise blood glucose. The glycemic load goes further by accounting for how many carbohydrates are actually in your serving, giving you a more complete picture of each food's blood sugar impact. Both measures are shown with their clinical category and a plain-English interpretation.
Formula
Worked example
A 150 g serving of rolled oats (GI 55) contains about 18 g of available carbohydrates. GL = 55 x 18 / 100 = 9.9 (Low GL), so despite the moderate-to-low GI, a normal bowl of oats has a very manageable impact on blood glucose.
What is the glycemic index?
The glycemic index is a ranking from 0 to 100 that measures how fast a carbohydrate-containing food raises blood glucose compared to pure glucose (GI 100). Foods with a low GI (55 or below) are digested and absorbed slowly, producing a gradual, modest rise in blood sugar. Medium-GI foods (56-69) cause a moderate rise, while high-GI foods (70 or above) are digested quickly and spike blood glucose rapidly. The concept was developed in the early 1980s by Dr. David Jenkins and colleagues at the University of Toronto, and the international GI database is maintained by the University of Sydney.
Why glycemic load matters more than GI alone
The glycemic index does not account for how much of a food you actually eat. Watermelon has a high GI (76) because its sugars absorb quickly, but a standard slice contains very few carbohydrates - so the glycemic load is low. Glycemic load (GL = GI x grams of carbs in the portion / 100) captures both dimensions: how fast glucose enters the blood and how much enters. A GL of 10 or below is low, 11-19 is medium, and 20 or above is high. White pasta has a moderate GI of around 49 but a large bowl with 54 g of carbs delivers a GL of 26, firmly in the high category. This is why GL is the more practical tool for everyday meal planning.
Factors that change a food's glycemic index
The GI of a food is not fixed. Cooking method has a large effect: al dente pasta has a lower GI than overcooked pasta because the starch granules are less broken down. Ripeness raises GI in fruit - an unripe banana is around GI 30, a fully ripe one is around 62. Processing matters too: rolled oats (GI 55) convert to a much higher GI in instant oats (GI 79). Cooling cooked starches such as rice or potatoes forms resistant starch, lowering the effective GI. Eating high-GI foods as part of a mixed meal containing protein, fat, or fiber also reduces the overall glycemic response.
Using the GI and GL for blood sugar management
Research consistently links low-GI diets with improved long-term blood glucose control in people with type 1 and type 2 diabetes, as measured by HbA1c. Low-GI diets also tend to reduce LDL cholesterol and promote greater satiety, which can support weight management. Choosing mostly low-GL foods over the course of the day - rather than obsessing over individual items - is the most practical strategy. High-GI foods like white bread or sports drinks are sometimes useful for athletes needing rapid glucose replenishment, but for most people in everyday settings, lower-GL meals support steadier energy and better metabolic health.
GI and GL categories at a glance
| Measure | Low | Medium | High |
|---|---|---|---|
| Glycemic Index (GI) | 55 or below | 56 to 69 | 70 or above |
| Glycemic Load (GL) | 10 or below | 11 to 19 | 20 or above |
Cut-offs from the international GI database (University of Sydney) and Diabetes Care guidelines.
Frequently asked questions
What is the difference between glycemic index and glycemic load?
The glycemic index (GI) measures how fast 50 g of digestible carbohydrates from a food raise blood glucose compared to pure glucose. The glycemic load (GL) adjusts for the amount of carbohydrates in a real serving: GL = GI x carbs in portion (g) / 100. A food can have a high GI but a low GL if the carb content per serving is small. Watermelon (GI 76, GL about 5 per standard slice) is the most-cited example. For everyday meal planning, GL is the more useful number.
What is a good glycemic index for foods?
Foods with a GI of 55 or below are classified as low GI and are generally better for blood sugar control. Examples include most legumes, many fruits, whole grains such as barley and quinoa, and dairy products. Medium-GI foods (56-69) like brown rice, sweet potato, and whole-wheat bread are acceptable in moderate portions. High-GI foods (70 or above) like white bread, instant oats, and most refined cereals are best eaten in smaller portions or combined with protein and fat to lower the meal's overall glycemic impact.
Does cooking change the glycemic index?
Yes, significantly. Longer cooking breaks down starch structures, raising GI. Al dente pasta has a lower GI than overcooked pasta. Cooling cooked starchy foods such as rice and potatoes then refrigerating them increases resistant starch content, which lowers the effective GI when the food is later reheated. Baking versus boiling a potato, for example, raises GI from about 78 to 85.
Is low GI always better for people with diabetes?
A predominantly low-GI diet improves HbA1c and reduces blood glucose variability in people with type 1 and type 2 diabetes, according to multiple meta-analyses. However, total carbohydrate intake, overall calorie balance, and individual glucose responses all matter. Some people respond differently to the same food. A low-GI food that is eaten in a large quantity can still produce a high glycemic load and a significant glucose rise. Combining GI knowledge with portion awareness and regular blood glucose monitoring gives the best results.
Why is glucose used as the reference food for GI = 100?
Glucose is pure digestible carbohydrate that is absorbed directly into the bloodstream, producing the fastest possible blood sugar rise. Using it as the 100-point reference makes GI values comparable across laboratories worldwide. Some older studies used white bread as the reference (white bread = 100), which produced slightly different numbers, but the glucose-based scale (glucose = 100) is now the international standard.
Can I lower the GI of a meal by combining foods?
Yes. Adding protein, fat, or fiber to a high-GI food slows gastric emptying and glucose absorption, reducing the effective glycemic response. Eating white rice with beans, vegetables, and a protein source produces a substantially lower blood glucose rise than white rice alone. Vinegar-based dressings and intact grain structures (like true sourdough) also lower effective GI. The glycemic response of a mixed meal is roughly a weighted average of the individual foods, weighted by their carbohydrate contributions.