This should be simple. You have a trash can. You need a bag that fits inside it. And yet, somehow, millions of people are walking around with bags that are too big, too small, or too short – bunching at the bottom, slipping down the sides, or stretching so tight that one chicken bone punctures the whole thing.
Let's fix this. Permanently.
The trash bag industry uses gallon sizes, which sounds straightforward until you realize that your trash can probably doesn't have its gallon capacity printed anywhere useful. So the first step is figuring out what you actually have.
Here's the quick method: measure the diameter of your can's opening (across the top) and the height from the bottom to the rim. That's it. You don't need to calculate the volume yourself – just match those two numbers to the right bag size. If your can is round, measure the diameter. If it's rectangular, measure the width and depth.
The four standard sizes cover about 95% of household bins:
4-gallon bags fit cans that are roughly 10 inches wide and 12 inches tall. These are your bathroom wastebaskets, office bins, and small bedroom cans. Most people underestimate how many of these they go through. If you have three bathrooms and two bedrooms, that's five small bins cycling through bags every few days.
8-gallon bags are the underrated middle child. They fit cans around 14 inches wide and 18 inches tall – the kind you find in bedrooms, laundry rooms, and smaller kitchens. A lot of people stuff a 13-gallon bag into an 8-gallon can and end up with a bag that's flopping over the sides like a sad hat. Don't do that.
13-gallon bags are the workhorse. The tall kitchen bag. If you have a standard kitchen trash can – the kind with a step pedal and a lid – it's almost certainly a 13-gallon. These cans are typically about 16 inches wide and 24-26 inches tall. This is the size most people think of when they think "trash bag."
30-gallon bags are for the big bins: outdoor cans, garage cans, large utility bins. These cans are usually 20+ inches wide and 30+ inches tall. If you're using these indoors, you probably have a large family or a very specific situation (like a party cleanup or a renovation project).
Now here's where most people go wrong: they buy by price instead of by fit. A box of 13-gallon bags is cheaper per bag than a box of 8-gallon bags, so people buy the bigger size and use it everywhere. The result? Wasted plastic in the small bins and bags that don't sit right. It's a false economy.
The other common mistake is ignoring thickness. Bag thickness is measured in mils (one mil = one thousandth of an inch). Most cheap bags are 0.5-0.7 mil. That's fine for dry waste – paper, packaging, tissues. But the moment you put anything wet, sharp, or heavy in the bag, you need at least 0.9 mil. For kitchen bags specifically, where you're dealing with food scraps, liquids, and occasional broken glass, going below 0.9 mil is asking for trouble.
Here's a pro tip that most people miss: the bag should be 4-6 inches taller than your can. That extra height is what folds over the rim and keeps the bag in place. If the bag is exactly the same height as your can, it'll slip down the moment you push something in. If it's way too tall, you'll have excess plastic bunching up inside the can, taking up space.
Another thing worth mentioning: drawstring vs. flap tie. Drawstring bags cost a bit more but they're overwhelmingly worth it for any bag you'll be carrying. The drawstring cinches the top closed and gives you a handle to carry the bag without touching the sides. Flap ties are fine for small bathroom bins where you're just lifting the bag out and dropping it into a bigger bag, but for kitchen and outdoor bins, drawstring is the way to go.
If all of this sounds like more thought than you ever wanted to put into trash bags – that's kind of our point. At LAST BAG, we built a 30-second quiz that figures out your sizes, matches you with the right bags, and ships them on a schedule so you never have to measure, compare, or remember anything again. One and done.
But if you're the kind of person who likes to understand things before you automate them (respect), now you have the full picture. Measure your cans, match the sizes, go with at least 0.9 mil thickness, and get drawstrings for anything bigger than a bathroom bin. That's the whole formula.