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Garbage Bag Size Calculator

Calculate the exact garbage bag width, height, and gallon capacity for any round or square trash can using interior dimensions and overhang preference.

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How the Garbage Bag Size Calculator Works

Finding the correct garbage bag size eliminates the frustration of bags that slip inside the can, tear under load, or waste plastic with excessive overhang. The garbage bag size calculator applies three precise mathematical formulas to match any trash can shape and interior dimension to its ideal liner — no guesswork, no wasted trips to the store.

The Core Formulas Explained

For a round trash can with interior diameter D (in inches), the bag width formula derives from circular geometry:

Bag Width (W) = (π × D) / 2 + Ew

A flat bag, when expanded, forms a cylinder whose flat width equals half the circumference (πD/2). The extra term Ew — typically 2 to 4 inches — accounts for seam allowance and easy insertion. For a standard 13-gallon kitchen can with a 12-inch interior diameter: W = (3.14159 × 12) / 2 + 3 ≈ 21.8 inches. Rounding up to 22 inches matches the industry-standard 13-gallon liner sold in every grocery store.

For a square or rectangular can, the formula uses the perimeter instead: W = (4 × side) / 2 + Ew = 2 × side + Ew. A 10-inch square office bin therefore needs W = (2 × 10) + 3 = 23 inches of flat bag width.

The bag height formula adds a critical overhang allowance to the interior can height:

Bag Height (H) = Hc + O

Here Hc is the interior can height and O is the overhang preference. A 3-inch overhang provides a minimal fold-over; 6 to 8 inches allows a secure knot before carrying to the curb. A 20-inch-tall kitchen can with a 4-inch overhang preference requires a 24-inch-tall bag.

The volume formula converts interior geometry to the gallon measurement printed on every bag box:

V (gallons) = π × (D/2)² × Hc / 231

The divisor 231 is the exact number of cubic inches in one U.S. liquid gallon, as standardized by NIST Special Publication 1020: Guide for Labeling Consumer Packages. For a 12-inch-diameter, 20-inch-tall can: V = 3.14159 × 36 × 20 / 231 ≈ 9.78 gallons, confirming the labeled 10-gallon capacity and validating the formula against real-world products.

Input Variables and Their Impact

  • Can Shape: Round cans use the circumference-based formula; square cans use the perimeter formula. Misidentifying the shape typically results in a bag 2 to 4 inches too narrow, causing it to slip inside the rim during use.
  • Can Diameter or Width: Always measure the interior top opening, not the exterior. A 13-gallon kitchen can typically measures 11.5 to 12.5 inches inside; a 33-gallon outdoor bin measures roughly 18 to 20 inches. Exterior dimensions include base thickness and molded housing that inflate the number by 1 to 3 inches.
  • Can Height: Measure interior depth from the base to the rim. Exterior height includes the base platform and lid seat, making it unreliable for liner calculations.
  • Overhang Preference: A 3-inch overhang barely holds the bag over the rim for light dry waste. Heavy or wet waste warrants 6 to 8 inches. According to published garbage bag sizing references, most households prefer 4 to 5 inches as a practical all-purpose overhang.
  • Waste Type: Light paper waste needs only a 0.35-mil liner. Wet kitchen waste — food scraps, coffee grounds, liquids — requires 0.9 to 1.2 mil. Sharp yard debris and construction materials demand 2 to 3 mil contractor-grade bags. The calculator adjusts thickness recommendations accordingly.
  • Output Metric: Switch between bag dimensions (width × height in inches), volume in gallons, or recommended mil thickness to match whichever specification appears on the packaging at your local store.

Real-World Sizing Examples

  • 2.6-gallon bathroom bin (round, 7-inch diameter, 11-inch tall): W ≈ 14 in, H ≈ 15 in. Standard small 4-gallon bags provide a comfortable fit with minimal excess.
  • 13-gallon kitchen can (round, 12-inch diameter, 24-inch tall): W ≈ 22 in, H ≈ 28 in. The most common household liner size in North America.
  • 32-gallon outdoor toter (round, 18-inch diameter, 28-inch tall): W ≈ 32 in, H ≈ 33 in. A 33-gallon heavy-duty bag at 1.5 mil or higher handles yard and food waste safely.
  • 95-gallon wheeled cart (round, 26-inch diameter, 45-inch tall): W ≈ 45 in, H ≈ 50 in. Requires a 95-gallon contractor liner for secure containment of full-week household waste.

Why Accurate Sizing Reduces Waste and Cost

Undersized bags tear under load, force double-bagging, and double plastic consumption per haul. Oversized bags bunch at the bottom, reducing effective usable capacity by up to 30% and creating odor-trapping air pockets. For commercial properties, accurate liner sizing carries direct financial consequences: municipalities such as Seattle calculate disposal fees by container volume, where each step up in bin size incurs a distinct rate — making oversized liners that force a larger container a measurable budget liability, as detailed in the Seattle Public Utilities Commercial Garbage Rate Guide. Matching bag to can keeps both material costs and disposal fees at their minimum.

Reference

Frequently asked questions

What size garbage bag fits a standard 13-gallon kitchen trash can?
A standard 13-gallon kitchen trash can with a 12-inch interior diameter and 24-inch interior height requires a bag approximately 22 inches wide and 28 inches tall. Most brands label these as tall kitchen liners. Look for box dimensions of 24x27 or 23x28 inches — both fit standard models with 4 to 5 inches of overhang for folding over the rim or tying a secure knot when the bag is full and ready for removal.
How do I measure my trash can to find the right garbage bag size?
Measure the interior top opening — the diameter for round cans or the side length for square cans — and the interior depth from the base to the rim. Never use exterior measurements, which include base thickness and decorative housing and typically run 1 to 3 inches larger. Multiply the interior diameter by 3.14159, divide by 2, and add 3 to 4 inches to get the correct flat bag width. Then add 4 to 6 inches to the interior depth for adequate overhang at the rim.
What does bag width mean on garbage bag packaging?
Bag width on packaging refers to the flat, folded width of the liner as it comes off the roll or out of the box — not the open circumference. When the bag expands into a cylinder, its interior circumference equals exactly twice the labeled flat width. A bag labeled 22 inches wide opens to a 44-inch circumference, fitting a round can up to approximately 14 inches in diameter. Always compare the calculator's flat-width result directly to the number printed on the box to confirm a match.
How much overhang should a garbage bag have over the trash can rim?
Overhang is the extra bag material that drapes over the outside of the can rim, preventing the liner from slipping inside during use. A minimum of 3 inches keeps the bag securely in place for light dry waste. For heavy or wet waste such as food scraps, liquids, or yard clippings, 6 to 8 inches of overhang is strongly recommended — this extra material provides enough slack to tie a firm double-knot before lifting the full, heavy bag without risking a tear at the rim line.
Does the type of waste affect which garbage bag size or strength to choose?
Yes — waste type directly determines the required mil thickness alongside the dimensional fit. Light office paper and dry recyclables need only a 0.35 to 0.5 mil liner. Wet kitchen waste including food scraps, coffee grounds, and liquids requires 0.9 to 1.2 mil. Sharp materials such as broken glass, scrap metal, thorny branches, or construction debris demand 2 to 3 mil contractor-grade bags. Selecting a bag that is too thin for the waste type results in punctures, tears, liquid leaks, and potential hygiene or safety hazards during handling and transport.
Can the same garbage bag size fit both a round and a square trash can of the same volume?
Not reliably, because volume does not determine the required bag flat width — perimeter does. A 12-inch-diameter round can has a circumference of about 37.7 inches and needs a 22-inch flat-width bag. A 10-inch square can of similar volume has a 40-inch perimeter and needs a 23-inch flat-width bag. Though their gallon capacities are nearly identical, the required bag widths differ by roughly an inch. Running the garbage bag size calculator separately for each container shape ensures a snug, slip-free fit every time.