Magnesium in oats: dry weight, cooked portions and absorption

Keep dry and cooked entries separate

USDA SR Legacy 2018 lists dry regular/quick, unfortified oats at 138.0 mg magnesium per 100 g. A hypothetical 40 g dry portion provides 55.2 mg. Oatmeal cooked with water without salt has 27.0 mg per 100 g; its 234 g reference cup provides 63.2 mg. These are separate food records, not a measured before-and-after experiment on one batch. [1]

Some dietary magnesium is absorbed, not all of it

NIH ODS estimates that roughly 30–40% of magnesium from food and beverages is absorbed in general. That is not an oat-specific absorption measurement and should not be used to promise an exact absorbed amount from a bowl. Food composition tells you the amount present; it does not directly measure an individual’s uptake. [2]

A hypothetical oatmeal log

Record a 40 g dry-oat portion as about 55.2 mg magnesium before considering additions. If you instead weigh 200 g of cooked oatmeal matching the cooked entry, its estimate is 54.0 mg. Milk, nuts or other ingredients need separate entries. Do not count the same oats once dry and again cooked. [1]

Hypothetical example — choose one matching basis for an intake entry
Food and chosen amount	Magnesium estimate
Dry unfortified oats, 40 g	55.2 mg
Oatmeal cooked with water, 200 g	54.0 mg

Magnesium in oats: dry weight, cooked portions and absorption — original article outline diagram — Original editorial diagram of this article’s sections; no product photograph or clinical finding is depicted.

Sources for this article

USDA FoodData Central — SR Legacy April 2018 food composition dataset
Source consulted: 2026-09-20. This is a reference resource, not a claim that we conducted the studies or tested a product.
Magnesium - Health Professional Fact Sheet
Source consulted: 2026-09-20. This is a reference resource, not a claim that we conducted the studies or tested a product.