Baking
All-Purpose Flour
All-purpose flour is the single most-used ingredient across US home baking, and it's also the ingredient where an inaccurate conversion causes the most damage — a cup measured by scooping instead of spooning-and-leveling can be 15-25% heavier than the recipe intended, easily enough to turn a tender cake dense or a cookie tough.
This hub page brings together everything this site knows about all-purpose flour: its exact conversion figure (120g per cup, spooned and leveled), how it compares to bread flour and cake flour, real storage guidance (6-8 months at room temperature, up to a year sealed, up to 2 years frozen), and the genuine spoilage signs — musty or rancid smell, clumping, and visible pantry pests — worth checking for in a bag that's been open a while.
Because it's such a foundational ingredient, all-purpose flour doesn't have a listed substitute on this site in the same way an ingredient like buttermilk does — the closer question for flour is usually which OTHER flour a recipe should use (bread flour for chew, cake flour for tenderness), which is covered on its dedicated conversion page rather than as a substitution.
All-purpose flour is the single most-used baking ingredient in US home cooking, milled from a blend of hard and soft wheat specifically to strike a middle ground of protein content — versatile enough to work reasonably well in bread, cookies, cakes, and thickening sauces, even though a dedicated bread or cake flour would outperform it for any one of those jobs specifically.
"All-purpose" is a somewhat US-specific category — UK "plain flour" is a close but not perfectly identical equivalent, generally sitting at a slightly lower protein content, a genuine consideration when converting a British recipe rather than assuming the two flours are chemically identical.
Because flour is usually the single largest ingredient by weight in a baked good, getting its measurement wrong distorts a recipe's ratios more than a similar-sized error in almost any other ingredient would — scooping the measuring cup straight into the bag routinely packs in 15-25% more flour than the recipe's author had in mind, which shows up as a heavier crumb, a tougher chew, or a cake that just doesn't rise the way it should.
All-purpose flour's rise to dominance as a household staple is a relatively modern development, made possible only once industrial milling technology could reliably blend and standardize flour at a national scale — for centuries before that, flour was more commonly milled and used locally with far less consistency from one region to the next.
Frequently asked questions
What's the single most useful thing to know about measuring all-purpose flour?
Spoon it into the measuring cup and level it off with a straight edge — never scoop directly from the bag, which compacts extra flour into the cup and can add 15-25% more than a recipe intends.
How long does an opened bag of all-purpose flour actually last?
Roughly half a year to eight months left on the counter, stretching to about a year if the container seals tightly, and up to two years in the freezer — on the longer end for anything tracked on this site, mostly thanks to how little oil it contains.
Is there a good substitute if I run out of all-purpose flour?
It depends what you need it for — bread flour works for yeast breads (denser result in tender bakes), and a cake-flour approximation exists in reverse, but there's no single universal substitute the way there is for an ingredient like buttermilk.
Is there a difference between US all-purpose flour and UK plain flour?
They're close enough to be treated as equivalent in most home baking, though protein content can vary slightly by country and brand — for a recipe where the difference matters, checking the specific brand's stated protein percentage is more reliable than assuming an exact match.
What's the fastest way to check if my flour is still good?
Smell it — fresh flour has almost no odor, while flour that's starting to turn has a musty or faintly rancid smell; that's a quicker check than trying to estimate its age from memory.
Is there a printable version of this ingredient's conversion figures?
The Kitchen Conversion Pack product bundles this and every other sourced conversion figure on the site into one printable reference sheet, for anyone who wants a physical copy rather than looking each ingredient up individually.