Figuring out the doses for meal-related insulin can be a challenge, and there are a lot of different approaches you can take. Basically, you're trying to match the amount of insulin you inject with what your body will need to deal with the rise in glucose that will occur with your meal. If you eat a high-carbohydrate meal, you're going to need a lot more insulin than if you eat a meal with very few carbohydrates. That sounds simple enough, but in reality it can be very hard to figure out exactly how much insulin that is.

The gold standard in most people's minds for giving meal-related insulin uses carbohydrate counting. When you count carbohydrates, you tally up all the carbohydrates in the meal you're about to eat or have just eaten if you're taking the insulin at the end of the meal.

In order to determine how much insulin you need for each meal, you need to figure out your insulin-to-carbohydrate ratio, the amount of insulin your body needs to metabolize a certain amount of carbohydrate. This number varies from individual to individual, but the average person needs somewhere around 1 unit of insulin for every 5 to 10 grams of carbohydrate, so a 45-gram carbohydrate meal will require somewhere between 4 and 9 units of insulin. The person who needs 1 unit of insulin for every 10 grams of carbohydrate will require 4.5 units (45 grams divided by 10 grams/unit). With most standard insulin syringes or pens, you can give only whole units, so you'd have to round down to 4 or up to 5. If you need more insulin -- say 1 unit for every 5 grams of carbohydrate -- you'd divide 45 grams by 5 grams/unit to get 9 units. If you have an insulin-to-carbohydrate ratio of 1 to 5 and you eat a meal containing 40 grams of carbohydrate, you'd need 8 units. If you eat a meal containing 65 grams, you'd need about 13 units.