Find the trash bag size for your can: enter its diameter or sides and its height to get the flat bag width × length, plus the can’s capacity in gallons.

Measure the rim the liner must pass over and the can height. The result is a flat-liner estimate, rounded up.

Liner allowances
Blank means 4 in (10.16 cm). Zero adds no overhang.

Blank means half the diameter or the shorter box side. Override for your liner’s construction.

Related Calculators

How to Use the Trash Bag Size Calculator

Choose Flat bag dimensions or Can capacity, then select the can shape. For liner fit, measure the rim the bag must pass over. For capacity, use inside dimensions. The default liner overhang is4in (10.16cm); a blank bottom allowance uses half the round diameter or shorter box side. Optional entries remain active when collapsed. Check the maker’s closure and fit guidance.

Trash Bag Size Formula

The calculator converts entered inches or centimeters to a common basis. Box volume is length ×width ×height; round volume isπ ×diameter² ×height ÷4. Flat width is half the rim perimeter, and flat length is height +bottom allowance +overhang.

Vin³ = L × W × H
GUS = Vin³ / 231

Where:

  • L = trash can length in inches
  • W = trash can width in inches
  • H = trash can height in inches
  • GUS = estimated can capacity in US liquid gallons

How to Measure Your Trash Can

  1. Choose the shape and task; measure inside for capacity or around the rim for liner fit.
  2. Measure the diameter, square side, or both rectangular sides using the selected units.
  3. Measure the inside height from the bottom to the top edge where the liner sits.
  4. Enter the height, optional liner allowances when needed, and select Calculate.
  5. Compare both flat width and length with the product dimensions. The retained size and capacity lists are illustrative and do not guarantee fit or availability.

Example

If a trash can is 15 inches long, 10 inches wide, and 30 inches high, the estimated can capacity is:

US gal =(15 ×10 ×30) ÷231≈19.480519 US gal

Using those same dimensions for a liner estimate, flat width is25in and flat length is39in with the default5in bottom allowance and4in overhang. The first larger capacity label in the retained list is21USgal; neither that label nor can volume guarantees liner fit.

What the Gallon Result Means

The calculator gives you the container’s approximate internal capacity. That is the fastest way to narrow down bag choices, but actual liner fit also depends on:

  • Overhang: extra bag material above the rim helps prevent the liner from slipping.
  • Load type: bulky, sharp, or heavy trash may require a larger and thicker bag.
  • Can shape: tapered cans, swing-top bins, and bins with rounded corners may need more slack than the volume alone suggests.
  • Bag style: drawstring bags, flap-tie bags, and straight liners do not all fit the same way.

Common Trash Bag Capacity Ranges

Estimated Capacity Typical Use Selection Tip
4–8 gallons Bathroom, bedroom, small office bins Choose a slightly taller liner if you want the bag to wrap over the rim.
10–13 gallons Standard kitchen trash cans One of the most common household sizes; a little extra height improves fit.
20–30 gallons Utility rooms, medium commercial bins Useful when the can is deeper or receives heavier waste.
30–33 gallons Large office or janitorial cans A common step up when 20-gallon liners feel too tight.
39–45 gallons Large commercial containers Check thickness as well as capacity if the waste is dense or abrasive.
55+ gallons Outdoor, contractor, or drum-style use Capacity alone is not enough; strength and puncture resistance matter.

Tips for Better Bag Fit

  • Round up when in doubt: a bag that is slightly too large usually works better than one that is too tight.
  • Use interior dimensions: wall thickness can make outside measurements misleading.
  • Allow for folding: if you fold the liner over the rim, the bag must be taller than the can depth alone.
  • Consider waste volume growth: paper, packaging, and food containers trap air and can fill a bag faster than the raw can volume suggests.
  • Upgrade thickness for sharp items: cardboard edges, cans, or broken materials can tear a thin liner even when the gallon rating is correct.

Important Accuracy Notes

The volume model assumes a straight-sided cylinder or box. Tapered cans, rounded corners and usable fill level change capacity. Flat liner dimensions are practical estimates; seals, gussets, drawstrings, rim thickness and closure requirements can change the allowance. Verify fit with the bag maker.

Frequently Asked Questions

Should I match the bag size exactly to the calculated gallons?

Not always. Exact matching can work for light trash and straight-sided cans, but a slightly larger liner usually fits better because it provides slack at the rim and reduces tearing during removal.

Why does a bag with the right gallon rating still feel too small?

Bag fit is affected by more than container volume. A tall can, a wide rim, a tapered body, or a bulky load can all make a correctly rated bag feel undersized.

Is gallons or liters better?

Either is fine as long as you stay consistent. Gallons are common for household trash bag packaging, while liters are often used for metric product listings.

1US liquid gallon =3.785411784liters. Multiply US gallons by3.785411784 to get liters.

Using the calculator before buying liners helps reduce wasted money, poor fit, and ripped bags, especially when replacing an unfamiliar can or moving between brands with different size labels.