Reference:

www.mendosa.com/gilists

The glycemic index (GI) is a numerical system of measuring how fast a carbohydrate triggers a rise in circulating blood sugar—the higher the number, the greater the blood sugar response. So a low GI food will cause a small rise, while a high GI food will trigger a dramatic spike.

The glycemic load (GL) is a relatively new way to assess the impact of carbohydrate consumption that takes the glycemic index into account, but gives a fuller picture than does glycemic index alone. A GI value tells you only how rapidly a particular carbohydrate turns into sugar. It doesn’t tell you how much of that carbohydrate is in a serving of a particular food. You need to know both things to understand a food’s effect on blood sugar. That is where glycemic load comes in. The carbohydrate in watermelon, for example, has a high GI. But there isn’t a lot of it, so watermelon’s glycemic load is relatively low. Foods that have a low GI invariably have a low GL, while foods with an intermediate or high GI range from very low to very high GL. Therefore, you can reduce the GL of your diet by limiting foods that have both a high GI and a high carbohydrate content.

GL is calculated from the number of absorbable grams in a
"portion" X the GI.