Garbage Bag Size Calculator
Stop guessing at the store. Enter your trash can dimensions or its gallon rating and get the exact bag size to buy: flat dimensions, film thickness, and closure style.
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Two ways in: measure the bin, or start from a known gallon rating.
Measure inside the bin, bottom to rim.
Extra bag above the rim for tying. Auto-set from the use case; drag to override.
How garbage bag sizing actually works
Garbage bags are sold by gallons, but what really determines the fit is flat dimensions and film thickness. The gallon number on the box is a rough capacity rating. The two numbers that matter at the shelf are width by height in inches, measured with the bag lying flat, plus the mil thickness of the plastic film.
Gallons vs flat dimensions vs mil
Gallons tell you the intended bin capacity: a 13 gallon bag is made for the standard tall kitchen can. Flat dimensions (for example 24 by 28 inches) tell you whether the bag will physically wrap your bin: width is measured across the flat bag, height from the sealed bottom to the open top. Mil is one thousandth of an inch (0.001 inch) and measures film thickness, which controls strength: a 0.7 mil kitchen bag and a 3.0 mil contractor bag can share the same gallon rating while behaving like completely different products.
The two sizing formulas
A flat bag opens into a tube whose circumference is roughly twice the flat width. So for a rectangular bin, the required flat bag width is simply length plus width: a 10 by 14 inch bin needs a bag at least 24 inches wide flat. For a round can, the required flat width is 3.1416 times diameter divided by 2, which is half the circumference: a 15 inch diameter can needs a bag at least 23.6 inches wide flat. Required bag height is bin height plus overhang, the extra inches above the rim you need to fold the cuff or tie the bag shut. Always round up to the nearest standard size, never down.
Nominal gallons vs geometric gallons
Trash can ratings are nominal usable capacity, not the geometric volume of the container. A can rated 13 gallons typically holds more than 13 gallons of water if filled to the brim, and most cans taper toward the bottom. That is why two cans with the same gallon rating can need different bags. When dimensions and gallons disagree, trust the dimensions.
Film type matters as much as thickness
Two films dominate the market. High-density (HDPE) film is thin, crinkly, and more puncture resistant per mil; it is the film in most clear office can liners. Low-density (LDPE) film is soft, stretchy, and quiet; it is the film in most kitchen drawstring bags and all contractor bags. A 0.5 mil high-density bag can outperform a 0.7 mil low-density bag against sharp trash, so compare within the same film family when shopping by mil.
Drawstring vs flap tie vs twist tie
Drawstring bags have cords in a top hem that cinch the bag shut: the hygienic choice for kitchens because you tie and carry without touching the waste. Flap tie bags have built-in flaps you knot together: the cheapest option, fine for bathrooms and offices with light dry waste. Twist tie bags close with a separate wire tie and have no drawstring channel, which is a structural weak point, so they are the strongest choice for contractor and heavy-duty loads.
Standard garbage bag size chart
Consolidated from manufacturer charts. Dimensions vary by about 1 to 2 inches between brands; when in doubt, buy the larger of two close sizes.
| Gallons | Liters | Flat size (in) | Flat size (cm) | Typical use | Mil |
|---|
Mil thickness guide
| Thickness | Best for | Notes |
|---|---|---|
| 0.35–0.5 mil | Bathroom, bedroom, office | Light dry waste only: tissues, paper, wrappers. |
| 0.6–0.9 mil | Kitchen | The everyday range. Go 0.9 mil if you cook with bones or cans. |
| 1.0–1.2 mil | Heavy kitchen, diaper pails | Extra margin against wet, heavy loads. |
| 1.2–1.7 mil | Yard waste, garage | Resists twigs, leaves with stems, and garage clutter. |
| 2.0–3.0 mil | Contractor, construction | Survives nails, wood shards, and demolition debris. |
Worked examples
Example 1 — Standard tall kitchen can (rectangular)
Bin: 10 in long x 14 in wide x 24 in tall, kitchen use, 4 in overhang.
Bag width = 10 + 14 = 24 in. Bag height = 24 + 4 = 28 in. Bin volume = 10 x 14 x 24 / 231 = 14.5 gal geometric.
Answer: 13-gallon bag, 24 x 28 in flat, 0.6–0.9 mil drawstring.
Example 2 — Small round bathroom bin
Bin: 9 in diameter x 14 in tall, bathroom use, 3 in overhang.
Bag width = 3.1416 x 9 / 2 = 14.1 in. Bag height = 14 + 3 = 17 in. Bin volume = 3.1416 x 4.5² x 14 / 231 = 3.9 gal geometric.
Answer: 3-gallon bag, 15 x 18 in flat, 0.35–0.5 mil flap tie.
Example 3 — Outdoor can by volume
Can rated 32 gallons, outdoor events use.
32 gal is not a standard bag size; the smallest standard size at or above it is 33 gallons. 32 gal x 3.78541 = 121.1 L for reference.
Answer: 33-gallon bag, 34 x 39 in flat, 1.5–2.0 mil drawstring or twist tie.
Practical tips
- Measure the top opening, not the base. Most cans taper; the rim is the widest point and it sets the required bag width.
- When between sizes, size up. Excess bag folds neatly over the rim; a too-small bag stretches thin and splits.
- Match mil to the waste, not the room. A bathroom remodel needs contractor bags even though the room says bathroom.
- For cans without a standard match, check the height first. Width is the common failure: tall narrow cans often need a wider bag than their gallon rating suggests.
- Store a size cheat sheet where you buy bags. One photo of your bin with its dimensions on your phone ends the aisle guessing forever.
- Do not double-bag to fix a thin bag. One correct-thickness bag is cheaper and stronger than two thin ones.
Frequently asked questions
How do I calculate what garbage bag size I need?
Measure your bin, then convert to flat bag dimensions. For a rectangular bin, required bag width equals length plus width, because a flat bag opens to twice its width. For a round bin, required bag width equals 3.1416 times diameter divided by 2, which is half the circumference. Required bag height equals bin height plus overhang, the extra inches above the rim used for tying. Round both numbers up to the nearest standard bag size, never down.
What is the standard kitchen garbage bag size?
The standard tall kitchen bag is 13 gallons, measuring about 24 by 28 inches flat. It fits most tall kitchen cans, which are typically rated 10 to 15 gallons nominally. Choose a drawstring style in 0.6 to 0.9 mil low-density film for everyday kitchen waste.
What does mil mean for garbage bags?
A mil is one thousandth of an inch, or 0.001 inch, and it measures film thickness. Thicker film is generally stronger: bathroom bags run 0.35 to 0.5 mil, kitchen bags 0.6 to 0.9 mil, yard bags 1.2 to 1.7 mil, and contractor bags 2.0 to 3.0 mil. Note that material matters too: high-density film is thinner but more puncture resistant per mil, while low-density film stretches more before tearing.
Should the bag gallons match my trash can gallons?
Not exactly. Can ratings are nominal usable capacity, while the geometric volume of the can is larger, and cans taper toward the bottom. Always size by dimensions using the width and height formulas, then check that the bag gallon rating is close to the can rating. If dimensions and gallons disagree, trust the dimensions.
Drawstring vs flap tie vs twist tie: which closure should I choose?
Drawstring bags cinch shut with built-in cords, ideal for kitchens because you can tie and carry without touching the waste. Flap tie bags have built-in flaps you knot together; they are the cheapest option and fine for bathrooms and offices with light dry waste. Twist tie bags use a separate wire tie and have no drawstring channel, which is a weak point, so they are strongest for contractor and heavy-duty use.
How much overhang do I need above the bin rim?
Overhang is the extra bag length above the rim used to grip and tie the bag. Use 3 inches for bathroom and office bins, 4 inches for kitchen cans so you can fold the cuff over the rim, 6 inches for yard and outdoor bins, and about 12 inches for contractor bags that get pulled up and tied shut above a drum.
What is the formula for a round trash can?
For a round can, required flat bag width equals 3.1416 times the diameter divided by 2. For example, a 15 inch diameter can needs a bag at least 23.6 inches wide flat. Required height equals the can height plus your overhang. A 15 by 24 inch round can therefore needs roughly a 24 by 28 inch bag, which is the standard 13 gallon size.
What if my measurements fall between two standard sizes?
Always round up to the next standard size, never down. A bag that is slightly too large still works: the excess just folds over the rim. A bag that is slightly too small will stretch thin, split at the seams, or slip down into the can when loaded.
Can I use a regular kitchen bag for yard waste?
It is not recommended. Kitchen bags are 0.6 to 0.9 mil film designed for soft waste. Twigs, branches, and soil clumps will puncture them. Yard waste calls for 1.2 to 1.7 mil bags, and woody debris or mixed cleanup calls for 2.0 mil and up contractor bags.
Why do contractor bags cost so much more than kitchen bags?
Contractor bags use 2.0 to 3.0 mil low-density film, which contains roughly three times the plastic resin of a 0.7 mil kitchen bag, plus stronger seals to survive nails, wood, and demolition debris. You are paying for resin weight and puncture resistance, not just size.
Are compostable or biodegradable bags sized differently?
No, compostable bags follow the same gallon and dimension standards, so a 13 gallon compostable bag fits the same can as a 13 gallon plastic bag. They do have lower puncture and stretch resistance than conventional film, so avoid overfilling them and look for recognized certifications on the box rather than vague eco claims.
How do I convert liters to gallons for bag sizes?
Divide liters by 3.78541 to get US gallons. Common conversions: 15 liters is about 4 gallons, 30 liters is about 8 gallons, 50 liters is about 13 gallons, 120 liters is about 32 gallons, and 210 liters is about 55 gallons.
See also
Sizing bags for yard cleanup? Our compost size calculator helps you size the bin or pile that the yard-waste bags will feed.
Free tool by NRTechStudio