What is a nutrition facts label?

In one line

A nutrition facts label is the table on packaged food that lists the calories and nutrients in a set amount of the food, and what percent of a daily reference amount each one is.

What is a nutrition facts label?
The box on the back of a snack bag
On the back of snack and drink packages there is a box with names like calories, sodium and carbohydrate, plus numbers and %. What does this table tell you, and how do you read it?
In one line
A table of the nutrients in this food
A nutrition facts label is a table listing the calories and nutrients in a set amount of a packaged food. With it you can compare foods and judge how much of a day's eating this food makes up.
What is listed
Calories and eight nutrients
A Korean label lists calories along with sodium, carbohydrate, sugars, fat, trans fat, saturated fat, cholesterol and protein. Vitamins and minerals are added when the product lists or highlights them.
Sugars and saturated fat
'Of which' numbers inside a bigger item
Sugars are all the small sugars in the carbohydrate, such as glucose and table sugar, listed separately inside carbohydrate. Trans fat and saturated fat are likewise listed separately inside fat. So the carbohydrate number already includes the sugars.
How calories are counted
Carbohydrate and protein 4, fat 9
The calories on the label are counted as 4 kcal per 1 g of carbohydrate or protein and 9 kcal per gram of fat, added together. For the same weight, fat gives more than twice the calories of carbohydrate or protein.
The base amount
One package? 100 g? One piece?
A Korean label lists, by default, the amount in one whole package (total contents). Large products may list per 100 g (mL) instead, and products with several pieces may list per piece (unit contents). It helps to check this base at the top of the table first.
Reference amount per 1 serving
Not an amount you are told to eat
The 'reference amount per 1 serving' is set for each type of food based on how much people usually eat at one time. It is not a recommendation of how much to eat. When a label uses this amount as its base, it also lists the amount for the whole package.
What the % means
What percent of the daily reference value
The % next to a nutrient is its share of the '1-day nutrient reference value' for that nutrient. The reference value is an average daily intake standard; if sodium shows 30%, eating this food gives you 30% of the daily reference value. Calories and trans fat get no %.
What '0' means
Very small amounts are written as 0
A '0' on the label does not always mean none at all. Under Korean rules, sugars, fat and protein below 0.5 g, and calories below 5 kcal, are allowed to be written as '0'.
A common misunderstanding
Are the listed calories always for the whole bag?
No. Large products may list per 100 g. Labels that list per piece or per 1-serving reference amount also list the whole package. In a survey abroad showing a drink bottle that held several servings, when calories were listed only for one serving, about one in ten people got the whole bottle's calories right. When they were listed for the whole bottle, about nine in ten got it right.
Summary
Read the base amount at the top first
A nutrition facts label lists the calories and nutrients in a set amount of a packaged food, and the % is the share of a daily reference value. Whether the numbers are for the whole package, 100 g or one piece differs from label to label. Related terms: 1-day nutrient reference value, reference amount per 1 serving, sugars.