Oregon State's examples: about 2 lb a week for a household of 2–3, about 6 lb for 4–6.
Leaves, grass clippings or garden trimmings, by volume. The browns ratio below only applies to kitchen scraps, so for green material like fresh grass, include the browns you'll mix in with it.
Compost Bin Size Calculator
Work out how big a compost bin you need, and how many, from the scraps you actually throw out each week.
How Big Should a Compost Bin Be?
For a hot pile, size is the one thing you can't fudge. Nebraska Extension puts the minimum at 3 feet by 3 feet by 3 feet, one cubic yard (about 0.75 cubic meters, a 0.9 m cube), because anything smaller loses heat through its surface faster than the microbes make it. The same guide caps a pile at 5 feet tall by 5 feet wide (1.5 m), as long as you like, so air can still reach the center. [2] Those limits apply to each bin, so a three-bin hot setup is at least 9 feet (2.7 m) long.
A cold bin is different. It never has to heat up, so it has no minimum size. It only has to hold what you add before the oldest material finishes. The EPA says a pile left untended may take a year, so the calculator sizes a cold bin to a year of your material. [3]
Hot or Cold: Three Bins or One
Hot composting runs as a rotation. LSU AgCenter's three-bin plan has you add to the first bin and turn it weekly until it's full, move it to the second bin to cook until it cools to air temperature, then move it to the third to finish and cure. [4] The EPA calls three-bin systems a common model. [5] The catch: a hot batch has to be built to its full cubic yard at once, so you stockpile material until you have enough. Our start-a-pile guide walks through that first build, and the Pile Temperature Tracker tells you how it's cooking once it's built.
Cold composting takes one bin. You keep adding to the top and dig finished compost out of the bottom. It's slower and won't reliably kill weed seeds, but it's the realistic choice when your scraps trickle in.
Why Kitchen Scraps Alone Fill a Bin Slowly
Oregon State's worm-bin guide uses 2 pounds of kitchen scraps a week (0.9 kg) as typical for a household of two or three, and about 6 pounds (2.7 kg) for four to six. [6] Mixed food scraps are dense, about 42 pounds per cubic foot, so 2 pounds is only about a third of a gallon (1.35 liters). Add three parts browns, the EPA's ideal ratio, and the pile grows by about 1.4 gallons (5.4 liters) a week. [1]
At that rate, collecting one cubic yard for a hot batch takes about 142 weeks. Over a year the same household adds about 9.9 cubic feet (280 liters), and as it cures that shrinks to about a third, roughly 3.3 cubic feet (93 liters). That's why a cold bin about 2 feet (0.65 m) on a side is plenty for a small household, and why hot composting usually depends on fall leaves, grass clippings or garden waste to build a batch. Enter those in the yard-material field and watch the weeks drop.
Compost Bin Size FAQ
How big should a compost bin be?
For hot composting, each bin should be at least 3 feet wide, 3 feet deep and 3 feet tall (1 cubic yard, about 0.75 cubic meters), and no taller or wider than 5 feet, according to Nebraska Extension (G2222). Smaller piles can't hold their heat. A cold bin has no minimum size: make it big enough to hold about a year of the material you add.
How many compost bins do I need?
For hot composting, three: one you're filling, one that's composting, and one that's curing. LSU AgCenter (3838-K) and the EPA both describe this three-bin rotation. For cold composting, one bin is enough, since you keep adding to the same pile and dig finished compost from the bottom.
How long does it take to fill a compost bin?
Longer than most people expect. Two pounds of kitchen scraps a week (0.9 kg), about what Oregon State says a household of two or three produces, plus three parts browns comes to about 1.4 gallons (5.4 liters) a week. At that rate a 1-cubic-yard hot batch takes about 142 weeks to collect. A household making 6 pounds a week (2.7 kg) fills one in about 47 weeks. Yard material speeds it up a lot.
How much does compost shrink as it cures?
A lot. The EPA says a pile shrinks to about one-third of its original size by the time it's cured. That's why a cold bin sized for a year of material rarely fills up: the oldest layers keep settling as you add new ones on top.
How many browns do I need for my kitchen scraps?
The EPA recommends two to three parts browns (leaves, straw, shredded cardboard) to one part greens by volume, and calls three to one the ideal. Two pounds of kitchen scraps is about a third of a gallon (1.35 liters), so it needs roughly 0.7 to 1.1 gallons (2.7 to 4 liters) of browns.