Imagine a 1 lb steak contains N milligrams of of iron. After eating you'd absorb 0.2N milligrams. In 1 lb of spinach, there would be 2.5N milligrams of iron, an

Imagine a 1 lb steak contains N milligrams of of iron. After eating you'd absorb 0.2N milligrams. In 1 lb of spinach, there would be 2.5N milligrams of iron, and you'd absorb 6%, meaning you'd absorb (2.5 * 0.06)N milligrams, i.e. 0.15N milligrams. So clearly you need to eat more spinach to get the same amount of iron in the worst case. So you need to eat 33% more spinach in this case to get the same amount of iron. But some places list absorption of non-heme iron as low as 2%.