Trash bags are sold by capacity (gallons or litres) and by flat width × height. A bag lying flat has half the can’s circumference as its width, and the bottom of the bag spreads across the base of the can, so extra height is needed. 3–6 inches of overhang lets you fold the bag over the rim.
How to use the Garbage Bag Size Calculator
- Can shape
- Diameter / width
- Length (rectangular)
- Can height
- Overhang
Results update as you type, and every field accepts the units shown in its menu.
How it works
Choose the shape of the can, enter its dimensions and the overhang you want.
Tips
- Use the figures printed on your product or its manual when you have them.
- Round quantities up so you are never short.
- Measure twice before you buy anything cut to size.
- Everything runs in your browser – try different values to compare options.
Common mistakes to avoid
- Mixing units (inches and centimetres, mAh and Ah).
- Ignoring efficiency losses and safety margins.
- Treating rules of thumb as exact.
Inputs explained
| Field | What to enter |
|---|---|
| Can shape | Choose one: Round, Square, Rectangular |
| Diameter / width | Units: in, cm |
| Length (rectangular) | Units: in, cm |
| Can height | Units: in, cm |
| Overhang | Units: in, cm |
Example values
How the main result changes when Diameter / width changes and everything else stays at the example values above:
| Diameter / width (in) | Bag width (flat) (in) |
|---|---|
| 8 | 12.6 |
| 12 | 18.8 |
| 16 | 25.1 |
| 20 | 31.4 |
| 24 | 37.7 |
| 32 | 50.3 |
Formula
Rectangular / square can: bag width = (length + width); height = can height + overhang + width ÷ 2Round can: bag width = π × diameter ÷ 2; height = can height + overhang + diameter ÷ 2Worked example
Inputs — Can shape: Round; Diameter / width: 16 in; Length (rectangular): 20 in; Can height: 26 in; Overhang: 4 in.
Results — Bag width (flat) = 25.1 in; Bag height = 38 in; Can capacity = 22.6 US gal.
Frequently asked questions
What size bag fits a 13-gallon can?
A standard tall kitchen bag, about 24 × 27–28 in.
How do I measure a trash can for bags?
Measure the circumference (or diameter) and height, then add overhang.
What is the difference between gallons and bag size?
Gallons describe volume; width × height describe the flat bag – both should match the can.
What formula does the Garbage Bag Size Calculator use?
Rectangular / square can: bag width = (length + width); height = can height + overhang + width ÷ 2.