Garbage Bag Size Calculator
Enter the shape and dimensions of your trash can and the calculator will give you the exact bag width and bag height you need, along with the closest standard bag size sold in stores. Works for round, square, and rectangular cans in inches or centimetres.
How to find the right garbage bag size
Picking a bag by the gallon number on your can is unreliable because manufacturers rate can volume differently from bag volume. The correct approach is to measure your can and calculate the bag dimensions you need. For a rectangular or square can, the bag width equals the can width plus the can length (all four sides wrap around a bag that is folded flat). The bag height equals the can height plus a tie-off allowance (3-6 inches is typical) plus one quarter of the bag width to cover the bottom. For a round can, the bag width is half the circumference of the can opening, and the bag height is the can height plus the tie-off allowance plus the can radius.
Rectangular and square cans
A rectangular trash can measuring 11 inches wide and 14 inches long needs a bag that is at least 11 + 14 = 25 inches wide. If the can is 26 inches tall and you want 4 inches of overhang, the minimum bag height is 26 + 4 + (25 / 4) = 36.25 inches. Round up to 37 inches. A standard 13-gallon kitchen bag (24 inches wide by 27 inches tall) would be too narrow for this example - you would need at least a 30-gallon bag. This is the most common sizing mistake: checking the gallon label instead of measuring the can.
Round and cylindrical cans
A round bin with a 16-inch diameter has a circumference of 16 x 3.1416 = about 50 inches. When a bag is folded flat in the package, its flat width represents half the circumference it can open into, so you need a bag at least 50 / 2 = 25 inches wide. If the same bin is 24 inches tall, the minimum bag height is 24 + 4 (overhang) + 8 (half the diameter) = 36 inches. Many outdoor round cans are taller than their gallon size suggests, which is why round-can users often report that bags slip off or do not reach the bottom.
Bag thickness (mil rating)
Beyond size, the mil rating - the thickness of the plastic in thousandths of an inch - determines whether a bag will hold up to what you put in it. Light dry waste such as tissues and paper: 0.5-0.7 mil high-density bags work well. Everyday kitchen waste: 0.9-1.0 mil standard bags. Heavy or wet waste, yard trimmings, construction debris: 1.5-2.0 mil or higher. Industrial or sharp waste: 2.0-3.0 mil contractor-grade bags. A bag that is too thin will tear and leak; one that is too thick costs more without adding useful strength for light loads.
Standard garbage bag sizes
| Bag capacity | Bag dimensions (W x H) | Typical use |
|---|---|---|
| 4 gal | 17" x 18" | Small wastebaskets, bathroom |
| 7-10 gal | 20" x 22" | Office desk bins, bathroom |
| 13 gal | 24" x 27" | Kitchen trash cans (standard) |
| 20-30 gal | 30" x 36" | Medium kitchen or office bins |
| 33 gal | 33" x 39" | Large kitchen, outdoor bins |
| 45 gal | 40" x 46" | Outdoor wheeled 20-24 gal cans |
| 55 gal | 40" x 50" | Outdoor wheeled 32-35 gal cans |
| 65 gal | 50" x 48" | Outdoor wheeled 45-64 gal cans |
| 95 gal | 61" x 68" | Outdoor wheeled 95-96 gal cans |
Common retail bag sizes and the bin types they fit. The gallon rating on your can may differ from the bag gallon size - use the dimensions to match.
Frequently asked questions
Why does the bag gallon size not match my can gallon size?
The volume stamped on a can is measured by filling it with water. Bag volume is calculated from the flat bag dimensions, which includes the extra material that drapes over the rim. A 32-gallon wheeled outdoor can needs a 55-gallon bag because the bag must be tall enough to line the inside and fold over the rim. Always size by measuring the can dimensions, not the gallon label.
How much overhang do I really need?
Three to six inches (7-15 cm) is the standard recommendation. Too little and the bag slips into the can; too much and excess plastic bunches up outside the rim and looks untidy. If you tie the bag off rather than using a drawstring, four inches is usually enough to knot.
What is the formula for a rectangular trash can bag?
Bag width = can width + can length. Bag height = can height + overhang allowance + (bag width / 4). The width formula works because a flat bag has two layers; opening it into a rectangle uses all four sides. The width/4 term in the height formula accounts for the extra material needed to cover the flat bottom of the can.
What is the formula for a round trash can bag?
Bag width = (can diameter x pi) / 2, which is half the circumference. Bag height = can height + overhang + (can diameter / 2). The diameter/2 term (the radius) gives the bag enough extra length to cover the curved bottom of the can.
Should I round up or down when the exact size is not sold in stores?
Always round up. A bag that is an inch or two wider and taller than the minimum will drape cleanly over the rim and is far easier to remove when full. A bag that is even slightly too narrow will stretch, tear, or slip down into the can.
How do I measure a round can if I do not have a flexible tape?
Set a rigid ruler across the widest part of the opening from one inner edge to the other. That measurement is the diameter. Alternatively, wrap a string around the outside of the can, mark where it meets, and measure the string length - that is the circumference. Divide the circumference by pi (3.1416) to get the diameter.