Glycemic Index Calculator
Medically reviewed by Dr. Chhaya Makhija, MD, DipABLM — September 2026
Check whether a food is low, medium or high glycemic index (GI) and see what its GI means for a real-world serving. For meal and daily totals, use the dedicated Glycemic Load Calculator.
GI of the food on the glucose = 100 scale.
Total carbs minus fibre, for the portion you eat.
Glycemic index is measured in a way that quietly limits how useful it is: every food is tested at a portion containing 50 grams of available carbohydrate, regardless of how much food that actually requires.
For bread or rice that is a normal serving. For watermelon it is close to a kilogram. Watermelon's GI of around 72 sounds alarming until you notice that reaching the tested portion means eating far more than anyone does — and that a realistic slice contains so little carbohydrate that its effect on glucose is modest.
This is why glycemic index alone is a poor guide to real eating, and why glycemic load exists. GL multiplies the index by the carbohydrate in an actual serving, which reorders the rankings substantially: several high-GI foods turn out to have low glycemic loads at normal portions, and some moderate-GI staples turn out to matter more.
Neither figure survives contact with a mixed meal unchanged. Fat, protein, fibre, ripeness, cooking method and even cooling after cooking all shift the result.
Use the calculator below to check a food's band. Beneath it you will find how GI and GL differ, reference bands, and values for common foods.
How to Use This Calculator
- Enter the food's glycemic index on the glucose = 100 scale (use the reference table below or a published GI list).
- Enter the available carbs per serving — total carbohydrate minus fibre — for the portion you actually eat.
- Read the glycemic load and its low / medium / high band.
GL reflects a real serving's glucose impact better than GI alone. It guides food choice and is a complement to — not a replacement for — carbohydrate counting.
Glycemic Index vs Glycemic Load
The glycemic index ranks a carbohydrate food by how quickly it raises blood glucose compared with pure glucose (GI 100). But GI ignores portion size. The glycemic load fixes that by scaling GI to the actual grams of carbohydrate in a serving:
Example: watermelon has a high GI (~72) but few carbs per serving (~8 g) → (72 × 8) ÷ 100 = GL ≈ 6 (low).
Want the load of a whole plate, not just one food? The dedicated glycemic load calculator lets you add several foods, see a running daily total, and pick from a built-in table of 50+ glycemic load values.
GI and GL Reference Bands
| Category | Glycemic Index | Glycemic Load (per serving) |
|---|---|---|
| Low | ≤ 55 | ≤ 10 |
| Medium | 56–69 | 11–19 |
| High | ≥ 70 | ≥ 20 |
Lower-GL meals tend to produce smaller, steadier glucose rises, which can support insulin sensitivity over time.
Glycemic Index of Common Foods
Approximate GI values on the glucose = 100 scale (they vary by variety, ripeness and cooking):
| Food | Approx. GI | Band |
|---|---|---|
| White bread | ~75 | High |
| White rice | ~73 | High |
| Boiled potato | ~78 | High |
| Watermelon | ~76 | High |
| Banana (ripe) | ~51 | Low–medium |
| Rolled oats | ~55 | Low |
| Apple | ~36 | Low |
| Lentils / chickpeas | ~28–32 | Low |
| Whole milk | ~39 | Low |
| Peanuts | ~14 | Low |
How to lower a meal's glycemic load
Pair carbohydrate with protein, healthy fat or fibre; choose whole, less-processed grains over refined ones; keep carb portions modest; add acidity such as vinegar or lemon; and note that cooking and cooling starchy foods like potato, rice and pasta forms resistant starch that lowers the effective GL.
Limitations & Safety Notes
- GI is measured by feeding test subjects a portion containing 50 g of available carbohydrate. It says nothing about realistic portion sizes — that is what glycemic load is for.
- Published GI values carry wide confidence intervals. The same food varies by variety, ripeness, processing method, cooking time and even storage.
- A food eaten inside a mixed meal with fat, protein and fibre behaves differently from the same food tested alone.
- GI is not a measure of how healthy a food is, and it is not a measure of insulin demand — the food insulin index addresses that separately.
Frequently Asked Questions
How do you calculate glycemic load?
Multiply the food's glycemic index by the grams of available carbohydrate in your serving, then divide by 100. For example, a food with GI 64 and 30 g carbs has a GL of (64 × 30) ÷ 100 = 19.2.
What is the difference between GI and GL?
GI rates how fast a carbohydrate raises glucose, regardless of amount. GL accounts for both speed (GI) and quantity (carbs per serving), so it better reflects a realistic portion's effect on blood sugar.
What is a good glycemic load?
Per serving, a GL of 10 or under is considered low, 11–19 medium, and 20 or more high. Lower-GL choices generally cause gentler blood-glucose rises, but overall diet quality and total carbs still matter.
Does glycemic load replace carb counting for insulin?
No. For mealtime insulin, carb counting with your insulin-to-carb ratio is the standard. GL is a complementary guide to food choice. See our insulin-to-carb ratio calculator for dosing.
Which foods have a low glycemic index?
Most non-starchy vegetables, legumes (lentils, chickpeas, beans), most whole fruits such as apples and berries, rolled oats, dairy, and nuts are low GI (55 or under). Highly processed grains, white bread and rice, and many starchy foods like potatoes tend to be high GI.
Does cooking or ripeness change a food's glycemic index?
Yes. A riper banana has a higher GI than a green one, and longer-cooked or mashed starches raise GI versus firm, al-dente versions. Cooking then cooling potatoes, rice or pasta forms resistant starch that lowers the effective GI, even if you reheat them gently.
Sources
- Atkinson FS, Foster-Powell K, Brand-Miller JC. International tables of glycemic index and glycemic load values. Diabetes Care.
- Harvard T.H. Chan School of Public Health. Carbohydrates and blood sugar — glycemic index and load.
Written by Ryan Mitchell · Last updated: September 2026